What you are saying is (of course) correct. But that makes the posturing / marketing of Protonmail no less deceptive if not outright dishonest.
It can indeed be (cynically) argued that Protonmail is just a company like any other, which will just say / claim whatever it thinks it has to, to find itself a slice of the market and make a buck.
Nonetheless and even while that might actually be the case (I'm not sure), in "the good old days" (/sarcasm) citizens still had something like tar and feathers to deal with dishonest business practices. I wonder what do citizens / consumers actually have these days? Please don't respond with: "voting with our feet", because that is not how things work with deceptive marketing.