Volunteering & Volunteer Students

Today, a man I've only known for about 6 weeks (The Head of School where I've been volunteering.  It's a private school for dyslexic kids;  with no religious affiliations) handed me a card.  He said something like, "The kids love having you here and you've inspired them to read."  It was a nice thing to hear.  I shook his hand as I placed the card in my backpack.  Once he walked away, I pulled it out & opened the envelope.  I was floored, as it said:

As if that wasn't weird enough!  Inside was a $100 bill.  All of these thoughts went through my head.  Things like:  "Would it be rude of me to tell him I'm Jewish?"  "Would it be insulting if I gave him the money back?"  "Would it be too awkward to ask him why he gave me a religious card and money?"  "Is this his money or did the staff pitch in;  and do I need to thank all of them too?"

Well I ended up saying something generic, "Thank you, so much, for your generosity."  Then I left cuz the whole thing really creeped me out.