That was not 'the' alternative. Skype, Teams (which subsumed it), Jitsi (which we used as a partially remote team prior to the pandemic and then inexplicably switched from to Zoom during), Discord was just starting to leak out of gamer-sphere, I think Slack already had group video calls, etc.
In California where I live it was. Skype was used by virtually no one. Teams and Jitsi were minor players. Google meet did not yet have traction. Most companies were using WebEx.
So as you say, most were already using something non-Zoom, that's the up-thread point - where did Zoom come from.
Also I doubt Teams was a minor player, in usage maybe but not availability - it has a free tier I think but otherwise comes with O365, which is obviously not minor. Having it doesn't mean you use Teams, but it does mean that it ought to be an obvious choice if you suddenly, newly, have a need for a product like that, as so many companies did.