OP, if I understand it right, you asked the guy if he needed anything, he said he was good. You later donated to his charity and probably warmed his heart on his trip... Sounds like you did right in my book
I agree. You did good. Inviting him to stay over in your home or to share a meal would have been fine too.
As far as folks being insulted over being offered food. Just about any touring cyclist I have met is happy to accept hospitality in just about any form if it is offered out of friendliness or kindness. The offer of a place to stay or a meal should always be either accepted or declined graciously and with gratitude.
I have had quite a few folks put me up for the night, feed me, or offer to pay for my lunch and when at home I have done the same for other cyclists. It typically seemed to be from a desire to help someone doing something they admired or just to be a part of the trip in some way. The openness, generosity, and kindness of strangers is one of the nicest things about touring and is a wonderful thing to give and to receive.
As far as that "Predjudice against touring cyclists" thread goes... There was a lot on nonsense thrown around on that one IMO. I'd be very careful what I conclusions I made based on it.