Yep, I see this as a marketing move and nothing else. It's about the brand, not the device or "enterprise" users. LG could not afford to be the brand not participating, and whether they deliver specifically on the G6 doesn't matter. By the time it would get dropped for non-compliance (if it happens) the next model would be out.
Also, despite what the linked article says, the Enterprise program does not at all imply the G6 will get 8.1. The requirements are Android 7.0+ with "one letter upgrade" from the current shipping release, plus 90-day security updates. This means 8.0 qualifies. And I don't see any timeframe requirement for that upgrade.
Furthermore, it is not even a guarantee that the carrier-branded models will get the upgrades/patches. That is up to the carriers.
So, while it sounds good, I don't think it really means anything in real terms.