Stock Ai pitting last lap for fuel!?

doing a 15 lap race at indy, normal fuel use, and the AI all pitted in on the last 2 laps, i came from 23 to win..

Is this a bug?

 

I would suspect the basic setup.
Load the default setup and look how much fuel is filled and calculate how many laps you can drive with it.
If the AI runs into "low-fuel", short before of the end of a 15 lap race in your example, they will pit of course.

 

was default setup, same fuel as ai?

 

If everything uses the default settings, the AI uses the amount of fuel that you see in the garage menu, if you load the default setup.
But i don't know the minimum amount that the AI has to have before they are forced to pit.