I don't think that's what your guy was doing (considering how he was dressed!) but I know that my own behaviour on the bike can seem erratic to some sometimes. When I do intervals I ride extremely slowly, then as hard as I can for a minute, so I pass other cyclists, then I slow down again, etc. I never do that on busy roads, though, only where there is an extra wide shoulder, but I know it must seem bizarre to some because they have to pass me because I'm so slow and then ... I pass them again. Annoying I know.