He did, while including that they're trying to screw over clients, and implying they're a shady business in his email. Again, he could've asked this without making these accusations.
I agree, they should've disabled the "add staff" button.
He expressed his disapproval of one particular practice and I don't blame him. I think it's a shady feature too - getting people accustomed to a feature above their plan and then default-upgrading unless they take a particular step.
They have a solid policy for traffic spikes which is to be commended, but with something like adding staff, which is an active user decision, I think the method is reminiscent of dark patterns which this community tends to resent.
It would be standard practice to disable the "add staff" button after two users and alert the user to upgrade options. I can't think of a service that doesn't operate like this, actually.