Thought for discussion...
Although it appears it hit the apparatus, consider the possibility that maybe it hit the power lines down further from the transformer. If you follow what would have been the lines down the side of the highway (we have to extrapolate since we can't see for the rain) they would disappear from the line of sight of the camera, behind the fire apparatus. If a strike were to hit those, from the line of site of the camera, it would appear as if the fire apparatus was being hit.
Here is why I think this. If you watch it closely, the lightning arc sort dances from left to right (up the power line in the direction of the transformer?) I have seen this a couple of times. The transformer blew, which of course was not connected to the fire apparatus in any way. Why? If the lightning did indeed hit the lines out in front of the fire vehicle (from the line of sight of the camera) then the transformer explosion makes sense. Something else I have seen before, the lines being hit further down and blowing the closest transformer.
Also, the emergency lights kept flashing. That was a pretty intense strike. I would have possibly expected some electrical damage of the vehicle.
All the same, wicked lightning video!