The Top Bar was already open when I was an undergraduate. We used to go there to play on the pinballs and the arcade games (mainly Missile Command and Battlezone). I'd order a pint of lemonade and blackcurrant. There used to be gigs there by small, local bands. Blur played there before they became famous. The half that is now the Fusion eaterie was the Senior Common Room that only lecturers who paid a subscription and their guests were allowed to enter.
I don't know where whoever put this up got the idea that the Top Bar didn't appear until the 1990s, but a glance through the archive of student newspapers from the 1970s would quickly disabuse them of this impression.
I'd complain, but then they'd ask me to write a correct version, which would be work.