The thing people often forget about skinheads, is that there are different kinds:
The "evil" nazi skinheads
The anti-nazi skinheads who may or may not be communist skinheads
Old school skinheads who say they've got their roots from workers would listen to ska back in england, etc.
If you were with another girl, perhaps they were nazi-skinheads looking to -er- purify the race or something. But it was probably just a bunch of guys with shaved heads taking advantage of how "scary" they look to go and intimidate people, especially girls, since it gives them a sense of superiority.