How can this puzzle have a 1866 rating?

I assume that many players see that taking the bishop on a6 wins two pieces for the rook, which is usually an advantage, without realizing the bishop is defended by the queen. (I myself thought the bishop capture was the right move at first)

I just completed it perfectly and it was claimed to be 1779, which still seems rather high

You competed it perfectly because you knew i was a puzzle. In a game, not that obvious especially in short games. :)

I'm seeing a low 84 rating for the puzzle. Not sure what you're referring to.

Puzzles get ratings by how well people solve the puzzles. In this case, I assume most people saw they could take the bishop and win 2 pieces for the rook, but the pawn on e4 hangs at the end of the line, with d5 being attacked, and hard to defend.

But yeah, shouldn't be rated this high. Maybe, because it's rated this high, it makes people question the obvious move, and to make mistakes.

You have to be able to see the whole position. This is something 1300 lichess users are not capable of doing.

That's a bit disingenuous, I am rated well below 1300 yet I saw the puzzle and within 20 seconds had completed it perfectly.