Reply #2: tough call.

[some guy]

On the one hand, he was stopped and indicating he was going to turn, so you're fine to move into his lane.
Plus, he is responsible for making sure he can go forward if he changes his mind and decides to do that.

On the other hand, you have to be sure the lane is clear enough for you to move into, so even though you've passed him, you need to make sure he hasn't suddenly decided to go forward and is now occupying what you thought was empty space.

( You ought to have given yourself more clearance of him before you started to change lanes?)

I'd decide in your favor, since he was the one who apparently changed his mind, and thereby added a level of confusion to the situation.