Challenging an introverted atheist

[Drummer Guy]

I'm extroverted, so it's easier for me to respond in this kind of situation.  I find it's best not to debate with people, just ask them questions.  When a religious comment is directed at you, maybe just ask "Do you think that's an appropriate question to ask during company training time?"  If that makes him back off, good. If it makes him more bold then just don't go any further, and let the company know that this is happening with an outside contractor who is preaching while he is getting paid to train.