Yea, that'd also be like saying Edge and Brave aren't browsers either. They're just skins on top of Chrome. The browser is way more than its rendering engine.
Both Edge and Brave make deeper changes than are allowed on iOS, such as making their own decisions about which APIs to expose. Yes, they are mostly Chromium, but they are in a technical position to change anything they want in a way Apple prohibits.
(Disclosure: I work for Google, speaking only for myself)
(Disclosure: I work for Google, speaking only for myself)