Looks like an incursion by the dash 8 based on the comms record released by the government:
17:43:02 JAL516 Tokyo Tower (control), JAL516 spot 18
Tokyo Tower JAL516, Tokyo Tower Good evening. Continue the approach to Runway 34R (Runway C). Wind 320 degrees 7 knots. There is a departure plane
17:43:12 JAL516 JAL516 Continues approach to Runway 34R
17:43:26 DAL276 Tokyo Tower, DAL276 Taxiway C. heading towards stopping position
Tokyo Tower DAL276, Tokyo Tower Good evening. Please proceed to runway stop position C1.
DAL276 Runway stop position C1 DAL276
17:44:56 Tokyo Tower JAL516 Runway 34R No problem landing. Wind 310 degrees 8 knots
17:45:01 JAL516 Runway 34R No landing problems JAL516
17:45:11 JA722A The tower is on the JA722A C taxiway.
Tokyo Tower JA722A, Tokyo Tower Good evening. 1st. Please taxi to the runway stop position on C5.
17:45:19 JA722A Head to runway stop position C5. 1st. thank you
17:45:40 JAL179 Tokyo Tower, JAL179 Running to runway stop position C1
Tokyo Tower JAL179, Tokyo Tower 3rd. Please proceed to runway stop position C1.
JAL179 Run to runway stop position C1, ready for takeoff
17:45:56 JAL166 Tokyo Tower, JAL166 spot 21
Tokyo Tower JAL166, Tokyo Tower Good evening. 2nd, continue on approach to Runway 34R. Wind 320 degrees 8 knots. There is a departure plane. Please reduce speed to 160 knots
17:46:06 JAL166 Reduced speed to 160 knots and continued approach to runway 34R. Good evening
17:47:23 Tokyo Tower JAL166, please reduce speed to minimum approach speed
JAL166 JAL166
17:47:27 3 seconds of silence

The language used appears to be a little different to standard but the may be a google translate issue. Last time I left Japan it was from Haneda and iirc stop bars were in place on at least some of the taxiways, it’s a very cluttered airport with many lights at night.

Edit : Looks like stop bars and various taxiway lights were inoperable, that will be a big factor in the “why”

NOTAM J2253/23: Tokyo Haneda International Airport (RJTT)
J2253/23 NOTAMN Q) RJJJ/QLRAS/IV/NBO/A/000/999/3533N13947E005 A) RJTT B) 2312271500 C) 2402211500 E) REF AIP SUP 225/23 ITEM TWY:2,3,4,5,6,7,10,11,12,13,33,38,44,54 TWY-CL-LGT FOR M1,R1,W11(BTN W AND R1)-U/S TWY-CL-LGT FOR E10(BEHIND SPOT 53)-PARTLY U/S TWY-CL-LGT FOR D5-U/S TWY-CL-LGT FOR A(BTN W AND A2),A(INT OF W1),A1,A2(INT OF A),W1 -PARTLY U/S TWY-CL-LGT FOR A16-U/S TWY-CL-LGT FOR K(BTN SPOT 304 AND C),R(INT OF K)-U/S TWY-CL-LGT FOR R(BTN K AND Y),R(INT OF Y)-PARTLY U/S STOP-BAR-LGT FOR C1 THRU C14-U/S TWY-CL-LGT FOR T12,T14,Q,Q1,Q2-U/S TAXIING-GUIDANCE-SIGN FOR T12,T14,Q,Q1,Q2-U/S TWY-CL-LGT FOR C(INT OF C3),C(INT OF C5)-PARTLY U/S TWY-CL-LGT FOR T(BTN T2 AND SPOT 909),T(INT OF T4),T(INT OF T6) -PARTLY U/S TWY-CL-LGT FOR C3(INT OF RWY 16L/34R)-PARTLY U/S RAPID EXIT TWY INDICATOR LGT FOR D5-U/S

That transcript is a translation to English of a translation to Japanese of the actual transcript which was in English. The actual, official transcript has been posted in several places including Av. Herald and shows a much more standard phraseology.

One reporter in a snippet shown in the UK stated that he saw not a single item of hand luggage being carried by those who evacuated.

I just read that and it is better. In my days it would have been clear to taxi for a c5 intersection departure, hold short of the runway and this would have been on ground. Aircraft would then transfer to tower on approach to the holding point where a “hold short” instruction would be repeated.

The notam indicates centreline taxiway lighting was also u/s, contributing to the possible confusion in the cockpit of the dash 8.

What is the significance of this? Isn't it normal?

I would assume people are always told not to carry/bring anything during an emergency evacuation.

Compliance with the rule has been rare in recent times where an evac occurred, so it’s significant but not surprising that in Japan compliance is the norm. Interestingly it’s been revealed overnight that most left the aircraft in the first seven minutes, it took another 11 minutes for the captain to get the remainder out who were cowering in their seats frozen in fear.

JAL was complemented on their inflight safety video regarding hand luggage.

https://www.facebook.com/watch/?v=751326522049450

When an aircraft is certified they have to test the evacuation process/time with volunteer/paid PAX.

Is the certification time 5mins to evacuate ?

90 seconds is the certification time for most countries, that’s irrelevant to what happens in real life of course, it’s theoretical.