How is this rating possible? Is this person a sandbagger?

Or he's just really bad at actual games, or he's cheating on the puzzles by opening the game in a separate tab (surely lichess would be able to keep what game it's from hidden until after you complete or fail the puzzle, right?)

It’s entirely possible to be good at puzzles and not games. Puzzles you can take as long as you need to solve them, and bullet has a strong flagging component (like 1+0) where you can play lousy chess but make moves fast enough to flag others often.

Right - I have had a puzzle rating over 2300 before but it never seems to translate to great results in practical games. I think part of the issue is that in a puzzle you know there's a tactic to look for, and there's no psychological or time pressure. Another thing is that tactics tend to flow from superior positions, so if you're not good at positional chess, you might not get as many tactical chances in your games. Most of the tactics are higher rated than they should be because people just guess instead of properly evaluating and considering counter moves. If everyone spent at least five minutes on each tactic they'd be rated lower.

A 700 point gap is really weird though. A 1700 at bullet can’t be that bad at blitz. I’d think sandbagger but who knows. Usually when one rating is much higher than the others it is rapid and blitz.

Have you checked to see what his highest ratings were in blitz/rapid/classical and how quickly he went from that to 1000-ish?

@Developmentals No its not really weird, because again bullet has a huge flagging component that doesn't exist to such a strong degree in other time controls. You will not be able to maintain a good rating in blitz if you can't play well enough to capitalize on opponent blunders and avoid making many of your own, but you can absolutely maintain a good rating in bullet with just moving fast and lasting as long as you can before your opponent flags. And none of those ratings are high enough to suggest he needs to play well to last long.

-Jordan