Slightly misleading to say Angular is in decline when you group Angular 1 and 2+ together.
There's a library that has X number of users. The library authors release v2 of that library, and it's a total rewrite. If every single user of v1 adopted v2, then you'd still have X number of users (grouped together across v1 and v2). However, you now have X minus Y users across both -- which means that some users stopped using v1 and didn't start using v2.
Which means that the adoption of your library has gone down. Or, put another way, is in decline.
Now, you could make the case that Angular 1 and Angular 2 are totally different frameworks that don't have anything in common and so they should have their adoption metrics treated differently, but even Google doesn't make that distinction, since they call them both "Angular". So to say Angular usage has gone down is factually correct, according to the definition of "Angular" provided by the people who built and maintain Angular itself.
To argue that the conclusion is wrong because the definitions are wrong (read: not the same as the definitions you personally use) is kinda just playing semantic games.
The frameworks are radically different and the install base is likely very different as well. If AngularJS (v1) was growing in popularity it wouldn’t really tell you anything about Angular (v2+), in the same way that the fact that Ember seeing a slow and steady growth doesn’t tell you anything about Angular (v2+). They’re different frameworks with dramatically different conventions and install bases. If AngularJS AND Angular were both losing popularity, it would still be misleading to group them together as “Angular.” They’re just not the same thing.
Choosing to name the newer framework was, in retrospect, an extremely poor choice, especially since it alienated all AngularJS users since there was no good migration path at the time and everything was so different; it might have made some sort of marketing sense in the pre-React/Vue world that Angular (v2+) began its life in.