I'd probably greet and tell and offer to help.
Just me, and I'd try to look friendly and upbeat, so that even if he might have been embarrassed, hopefully it would be pushed aside by a jest or just a cheerful smile.
I've done similar things, helping a elderly lady who dropped her umbrella under her car, and was doing amazing yoga style moves trying to get it out with her arthritic body. Once it was a young man who couldn't lift his bag of dog food into his car trunk from the buggy. I'm not sure what was wrong with him, perhaps a bad back? Perhaps he had MS? Who knew? I knew he didn't seem able to do the task, so I stepped up and smiled and said "Hey. Want a hand with that?" And when he looked, I grinned bigger "Those bags are slick to grab when your hands are wet.. here.. " And I picked it up and put it in place. When he said thanks, I nodded and walked away with a "No trouble at all, hope next time, it's not so wet outside!"
Yeah.. he could have been Ted Bundy. He could have been my cousin I've never met. Who knew? I didn't.
You write very well. I did not think things through, and ponder on it. I just helped, and went on with my life. I didn't think about what it might mean to him, or how it relates to others that need help too. You are a more deep thinking person than I. I look forward to seeing the extended post.