Chess Analysis Board

Often the chess analysis board will call a move best for white when it shows an alternative move to have a higher point value. Why is this?

You have to look more than one move deep. Since Leela and Alpha Zero, analysis includes more than one move.

I don't understand that. If I'm white on move 7, and for move 8 the analysis computer gives three possible moves: Move one has a score of +3.71, and it calls this the best move. But, move two it gives a score of +4.21, but it doesn't call this the best move? If a move has a higher score, isn't that supposed to be the deciding criteria for if it's a better move?

Why don't you give an actual example with the game/moves in question. 

I didn't get a screenshot. I will next time. But it did seem multiple times like it labeled a move "Best Move", when one of the other moves it gave had a higher score.

I clicked the analysis button for one of the positions in a lesson.

So, which lesson is it? It should be pretty easy to get the PGN of the position. 

I've been playing with it again. I suspect this is my mistake:

1) The score numbers keep changing for a few moments as it calculates, and the rank of the alternative moves can change. I may have quickly chosen the current high move, but after after a few moments it would have slipped to the second highest.

2) The most likely explanation. For black it chooses the lowest score, not the highest. I may have picked the best move for white, the highest scoring one, then looked back at the screen, and in the top position, where that move was, is now a different variation, and this one will be the variation that is best for black, not white, so the lowest score.  

Yeah, I think the solution is pretty simple. It does always choose as best the highest number when it's whites move, but look back from the board moments later and the top variation now shows the lowest number, because it's calculating blacks best move. And for black, the best move is the lowest number, as positive numbers mean white has the advantage, and negative numbers mean black has it.