These are not necessary in error.
Fire Investigator Units act as both Fire Investigation and as a Patrol Car. The ARR picks the closest vehicle which qualifies.
If you want them excluded, you should pick the Custom Vehicle category instead.
That is true, however there should be an option in the vehicles to switch that off. I don't want to have them respond as those, and I do not want to create an extra vehicle category and assign it to all the units I'm going to add.