[ahmetmsft]

It probably calculates the path in advance (note the "please wait" indicator appears just after you hit 'Solve') then it follows the path with an animation that gives you exactly the impression that it never falls into a trap as it goes.

[lovegraphs]

That's right, it does a breadth-first-search from the end-point immediately upon clicking the end-point; it then traces the path from the start-point, following the parent-pointers set during the BFS, painting the DOM in the process.

[je42]

Not using A* ?