It's not false equivalence, we were talking about communications between people. Corporations don't write emails, people do. A corporation, big or small, is just a legal way of definining the property of people, and the people who work for it (who may or may not also own some of it) are people. Communications between them are communications between people.
What they're saying is that people deserve privacy, unless what they're doing has some relationship to making money, in which case they do not.
I mean yes and no...
But it's a vague nebula. Stuff like whistleblower protections, retention laws, 'piercing the corporate veil'....
Of course we're talking about communications between people, but the record of these communications is used to find fault with the company, usually, not with the individual people. I think that's a really important distinction.
So I agree with the person who said this was a false equivalence.
Corporations exist at the pleasure of the people; we can and should impose any and all requirements and restrictions on them necessary to ensure they do not amass too much power and act to the detriment of regular citizens. We've failed in that, and we see the negative consequences of that daily.