Honestly a pretty nifty way to detect if it's installed. I'm sure this can power a lot of nice features, like linking directly into adobe products if they're installed.
They implemented it in a way that it only responds with a valid image and a 200 status code, when the referrer is adobe.com. It's probably somewhat sane given the insanity that is the host files hack.
Agreed, at worst this is just vaguely icky feeling; realistically this is a nothing burger.
To exploit this kind of thing you'd either need to have access to someone's computer to change the hosts file yourself, pointing to a different IP address, or somehow gain control of Adobe's IP address and point it to a different server. For the former, if you have local root permission, you already own the machine, why bother with this slow of an option. And the latter is already such a takeover that the involvement of this hosts file change is basically irrelevant.