Prior to the fight and even before the black guy got on the bus, the old man was talking to a friend of his on the bus. The old man's mother had just died two days earlier and he was asking his friend to borrow money to buy some nice shoes for the funeral. When he said "I'll get my boy to shine them" it had nothing at all to do with the black guy who had just gotten on the bus and definitely not in reference to a 1920s shine boy. The black guy who, at that point was walking past the two men, only heard "I'll get my boy to shine them" and responded "why's it gotta be a black man who shines your shoes?" and walks to the back of the bus. The old man didn't understand what was said and moved to the back of the bus to ask, that's where the video starts. Listen in to the conversation from there.
In the interview with the old man after the fact, the old man doesn't even mention race, not even in reference to the black guy. The only time he mentions race at all was in the context of what the black guy said.
On a side note, here's an article about a 72 year old man who beat up a younger man who was trying to rob him, complete with a mug shot of the robber afterward.
http://boingboing.net/2009/07/02/elderly-retired-boxi.html