I suppose I'm doing exactly what you want to avoid here (guessing GP's meaning), but I think their meaning is really quite obvious and isn't that hard to guess. GP can contradict me if they feel I'm talking out of my back.

American Social Media corps are pretty heavily progressive-dominated, which is typically called "The Left-Leaning Bias", but that's a shame, because American "Leftism" is really a laughable low-dimensional projection of what actual leftism looks like. So anyways, because of this, progressive social media denizens reciprocate this preferential treatment by being free (as in bear) and dependable apologists, always defending said corporations whenever they arbitarily ban, censor or otherwise unfairly treat those with the wrong opinons, often employing the well-known phrase that GP quoted.

GP is implying that those people are about to discover the brutal truth that suppression tactics are perfectly symmetric and care not who employs it against whom.

For me, and I don't even use Twitter, it's clear.

GP means that those resorting to "freedom of speech is not for companies" are hypocrites. They're defending the right of companies to supress opinions on their services, not because they believe that's fair --actually they're anti-business-- but because they can pressure the companies, threatening their advertisers, so only opinions approved by them will show.

If Twitter goes private and stops depending on ads, they won't be able to exert such pressure and will lose that advantage. Even if Musk is totally fair with moderation, they're going to complain he's not censoring enough.