If they'd put a screenshot, that would then have been immediately clear to casual visitors.
My initial assumption was "this is gonna look like a typical OSS product, and not as polished as iOS or Android". A single screenshot would have dispelled that notion.
It is just Android. If you're familiar with the usual Material styling of Android, you're familiar with what Graphene looks like.
If they'd put a screenshot, that would then have been immediately clear to casual visitors.
My initial assumption was "this is gonna look like a typical OSS product, and not as polished as iOS or Android". A single screenshot would have dispelled that notion.
It looks about the same as stock android.