Swallowed creatures are considered Unseen Attackers. Yes or No?

Quote from Natrel>>

This is a RAW discussion. Always has been since the start of this thread. So yes: irrelevant.

No , no, no. This whole conversation started with your story about a "hostile DM" committing some grave jnjustice against you and your party. And you came here looking for support that your hostile dm made a bad call. The player SHOULD be unseen.

And everyone has been clear with you: your dm made the right call. 

Some, not all, but some have said your interpretation might have some truth behind it, if we're just arguing in a vacuum., but everyone agrees in an actual game, your dm's call was the right call.

If someone came in here in 2014 and said the rules allow a peasant railgun, the response would be similar: maybe a technical reading would support it, but no dm would allow it in their game.

Quote from Natrel >>

This is a RAW discussion. Always has been since the start of this thread.

In that case: even though I've previously posted support for your interpretation in this thread, you probably should be aware of the RAW at the beginning of the PHB and DMG (aka 'Rule 0'):

"the DM decides how to apply the rules" (DMG p.5) and
the DM oversees "how the group uses the game’s rules" (PHB p.7)

As a player, you were absolutely in the wrong in this instance (especially since this particular rule is clearly subject to interpretation). Had you been the DM, I would say the same to any player that argued against you on this at the table. That's how the rules work, especially when both interpretations have merit.