Bobert, I think you did the right thing. Two reasons:

1) I have met and worked with some older blues players, and many of them don't see themselves as 'stars'; they still see every venue as just another juke joint where they have to play to earn their drinks and a little cash. He probably saw you as just a fellow 'musicianer' (David 'Honeyboy' Edwards' term for us players) and was grateful for the help. Ditto because he was older and humble enough to realize his ear ain't what it used to be.

2) This is, to me, the more pressing reason... you needed to step in because there were probably plenty of people in that room who wouldn't even have known if the damned guitar was in or out of tune at all. You needed to set it right so the people in the room could actually hear what was supposed to be coming out of the instrument.

I've played too many rooms and watched too many performances where the audience were a bunch of people who wouldn't know F-sharp from sharp cheddar. All they know is that the person on stage is doing something they can't do, they think it's somehow magical, and they proceed to "woo-hoo!" at every given chance, knowing not whether what they are hearing is good, mediocre or utter ca-ca.

Kudos for trying to be kind and offering to do the right thing.