It's very simple.
Guessing means taking move you can't be 100% sure is correct. Mostly people guessing rely on probability or what is obvious (like human, you expect him to have 2 legs, or wheels, you expect it to be circular). But it doesn't have to be. That's still guessing.
With MLS, you're 100% sure.
Difference between SLS & MLS is just that you use other lines to exclude some options you are not sure about with SLS. Principal is same, you just take wider picture with MLS.
You take it from your perspective as it look to you as "trying all options", but many skilled and talented solvers just visualize it in brain.
For example, I can visualize Gomoku board in my head. When I was young, I could visualize the game so well, I could plan up to 15 moves upfront with several directions game could "go".
I play unflagged Minesweeper with 150+ clicks below 60 seconds, uncovering 381 tiles (480 - 99). Because I can click in a row because I have ~100 tiles around mouse pointer in L1 cache