The Simple Simon Brigade could have been attacking him because of his expensive clothes. They could have been attacking him because of his pointed wit. They could have been attacking him just because he's mayor. In the past that's been enough for attacks, physical and otherwise, on white mayors. If so, it really worked.
Idiots do idiotic things for lots of idiotic reasons.
Just look at what's going on in Washington. A president who is very popular with black Americans is the defendant in an impeachment trial that smells like a musty Confederate uniform. Senate Majority Leader Trent Lott and the most rabid prosecutor, Bob Barr, give speeches at meetings of the Council of Conservative Citizens - a direct descendant of the old segregationist White Citizens Council.