Hold on, the guy did not get an atpl, that's is obtained by filling in form 495 and paying $100. Besides under the award an instructor is defined as having a cpl or higher with the rating.
He studied advanced aviation theory, and would use that theory in his current role teaching students, e.g. Atpl met/human factors theory is transferable knowledge to even a ppl student.
Get tax advice on the following, if the advanced theory you studied which can be used in your current role as an instructor is a ligit claim. Also the additional question if the $100 fee to obtain the atpl is deductible.
My guess is first question will be yes, second question will be no. Get proper advice.