Freddie was just fucking around during the really crazy ass part of "Sheer Heart Attack". I think those were monitor speakers placed there just for him to topple for that purpose
He could also afford to replace anything that was actually broken beyond repair, but monitor and speaker stacks like that are built rather solidly and can take more than a reasonable amount of abuse and punishment. I'm guessing the most damage Freddie could inflict would be damage to the cable connections and maybe jarring the wiring, woofers or tweeters.
I've seen touring speakers get kicked, dropped, stood on, rattled up and down stairs and ramps, have water spilt on them, dragged, tipped over and they still keep ticking.
It's so funny, you can see Brian trying to stop Freddie by placing his foot against the speakers so Freddie can't push them over. And then after 7 seconds or so, Brian thinks 'ah...fuck it'. And walks away as Fred pushes them over