Regardless of whether you consider this action just, it is not gaslighting. Gaslighting has a specific definition, and this isn't it: https://en.wikipedia.org/wiki/Gaslighting
> manipulating someone so as to make them question their own reality.
That's what he did. Telling users it is their own fault that he had to take their names and sell them. You were causing issues, because you did not log in for three months.
Justifying your actions isn't gaslighting. Blaming someone isn't gaslighting.
Gaslighting involves presenting a false history of things that did not happen. There is real data here that there are a huge number of inactive accounts.
> The term may also be used to describe a person (a "gaslighter") who presents a false narrative to another group or person, thereby leading them to doubt their perceptions and become misled, disoriented or distressed.
A false narrative is not necessarily including a false history of things. He is spinning a false narrative by using facts, but presenting them in a way that is misleading. like a politician. He is inventing a problem ("dead accounts are a huge problem that is causing my valued users many issues") and presenting a solution for that new problem that is mainly benefitting himself. All social media platforms have a huge number of inactive accounts, but that's for some reason only an issue sometimes. For example when Elon Musk takes over Twitter. Generally these platforms welcome inactive accounts, because it is inflating their numbers. Now Durov wants more money and he is inventing a problem and pointing at the users as the culprit.
He is achieving two (edit: tree) things with that:
1) He is gaslighting users into believing that it is their own fault that they lost their account name, because they have not logged in for three months, when stealing account names is actually just an arbitrary decision that he made.
2) He is incentivizing occasional users to log in more often, so they can keep their name. I guess he can then later use these numbers to sell ad space: "Unlike on other platforms, our users are much more engaged.
That's what he did. Telling users it is their own fault that he had to take their names and sell them. You were causing issues, because you did not log in for three months.