I cant find anywhere where it states an infiltrator does anything to drillers but im currently in a situation where im attacking a base where an enemy has an infiltrator, i have 2 instances of attacks landing and the infiltrator is going to kill 10 drills per instance.

Do you have a general?

it is not a bug. it is just you being a unknown. your enemy has general that boost his every specialist had ability to kill 10 drill at specialist phase.
-case closed-