I am afraid the fire truck might have some level of responsibility, since it seems FAA ground vehicle guidance says:
AC No: 150/5210-20A - "Subject: Ground Vehicle Operations to include Taxiing or Towing an Aircraft on Airports"
https://www.faa.gov/documentLibrary/media/Advisory_Circular/...
“you must ensure that you look both ways down the runway to visually acquire aircraft landing or departing even if you have a clearance to cross.”
These trucks seem to have pretty good visibility from inside. Not sure if La Guardia model was the same: https://youtu.be/rfILwYo3sXc
Not arguing with the regulations, just pointing out that based on airport diagram[1], since the truck was crossing rwy on taxiway D, the CRJ was on the right approaching from behind. I have never been inside an airport firetruck, but I guess from the driver's seat the jet would be quite hard to see in this case.
[1]https://www.avherald.com/h?article=536bb98e