This is very unfortunate. It’s 2019 and companies still produce web pages that enable/disable features based on UA sniffing. I’d suggest using an extension (e.g. User-Agent Switcher for Chrome) to work around the problem.
The “snap” token was added to the UA string initially to allow Install Linux apps using the Snap Store | Snapcraft to identify unambiguously a system that knows how to handle snap:// links, to provide accurate installation instructions. This isn’t ideal, but it’s not something we can easily revert either.
Indeed. An extension to override the default UA string sounds like a good mitigation for privacy concerns.
That’s not quite correct. The app is running on whatever the host system is, but it has a very limited view of that system. The fact that the snap was built on Ubuntu is an implementation detail, even more so in the case of chromium which embeds and builds many of its dependencies at build time.