Any app can do app specific URLs on iOS to invoke particular apps with content. I would guess that Google apps detect the presence of Chrome and modify the URLs to be Chrome specific rather than generic https URLs. Its ok with Apple because that is a standard supported mechanism on iOS.
As a user who expects all https links to open within my default browser, Google's exploitation of this workaround breaks the guarantees I expect out of the OS.
There are a lot of other "features" that are technically feasible but not allowed on AppStore. This to me should have been on that list.
Good point. Yeah, I don't like it either. Thinking about it a bit more, I share your surprise that they allowed this. I guess they need it for google.com links to make things work together, but Apple could have told them non-google links should be opened in the default browser.
