You have a phone. People use the same phone together with a Google service and a security-related bug in the phone could be used to e.g. steal your Google password, therefore the phone's software is in-scope, no matter who made it or what it runs.
I see the sense of it, but it's weird to me too. What's not used together with Google? That's such a wide scope. But it's not a matter of security or marketing, the weirdness is in the wide usage. Kudos to Google for working on it.
IT does make me wonder...what...don't..they report? Why wouldn't they hold a few smaller items back, focus a little more on iOS exploits? It's just a "Be aware of the source" thought. Still a net positive.
But I'd be curious how strictly their 90 day disclosure policy applies to Google products, and if they are more willing to grant some leeway when a fix isn't pushed in time...
What would you have them do? Ignore the iOS vulnerabilities and leave the iOS users unprotected? That'd be a great look...
Second, this is a really bizarre complaint given this very submission is reporting on both Android and iOS. Even if there really was security research being done with the specific goal of negative marketing on competing products (a claim you make with no evidence, and continue to double down on with no evidence), this submission would be a very bad example of that.