That's simply not true.
Stick 100 Celtic & 100 Rangers fans in the same pubs across the city and it won't be pretty. Most pubs are either Celitc, Rangers or many don't even show the game. The State Bar for example is one of the busiest boozers in the town and they never show Old Firm games as it's too much hassle. There's plenty of others. No weatherspoons showed it either.
I watched it in Rhoderick Dhu (first 50 minutes anyway) before going to Firhill and they had shutters down during the game, only letters folk in who were there for kick off to avoid any idiots.
Having grown up in Ayrshire and seen what these games do to grown men, then i'm not surprised folk expected trouble.
I think the fact many people made an effort to watch at home etc, the result was as expected and it was wild weather made it calmer than normal. Don't think many expected trouble at the game. Last time i can recall that happening was when Rangers won the league at Parkhead.
It's the tubes in pubs etc that usually cause trouble. Especially in towns miles away from where the game actually is.