Ah right OK... gotcha... So... Rather than politically motivated, it was more about keeping the peace, containing the situation and making arrests subsequently, while gathering evidence during the protest?
Sounds like sensible policing to me. Not worth kicking off a full scale riot by stomping into a crowd in yer size 10s if the majority are behaving themselves.
It's a no-win situation for the police really. If they stormed in at the time, while the homecoming parade was passing, they'd have been risking an escalation of a "peaceful" organised protest into a full scale riot and they themselves would probably have been criticised for disrespecting those same troops.
It's not a new thing. Even back in the 70s and 80s, they'd do their utmost to keep the e.g. fascists separate from the anti-racism protesters. If it gets violent, they obviously have to leap in, but while everyone's relatively "peaceful" (even if outrageously offensive), they practice crowd control.
If you were standing on the street corner yelling abuse with yer mates, they'd probably lock you up and throw away the key. Unless you had a couple of hundred mates and you'd organised the protest in advance and kept the police fully informed