This is not necessarily true. Sometimes there are emultiple best moves, and in this case the order might be arbitrary depending on all sorts of hard to control

This is not necessarily true. Sometimes there are emultiple best moves, and in this case the order might be arbitrary depending on all sorts of hard to control things like thread interleavings and caching effects which can be affected even by other processes on the system. You could run it single threaded with no transposition table, but then you have a pretty shitty engine because modern engines are fundamentally designed around having a transposition table. Then you get situations where the top engine move might actually be a bad move.