Challenge. I can tell the difference between you and this bot. It is very hard to act like a bot every time, especially with regard to the awkward pauses it makes at very unhuman times. I'd bet you don't close your inventory after IDing, wait for about 500ms, then walk directly to the vendor. And I bet when you're walking back to the town portal, you don't walk to the dead center of the TP before you use it.
EDIT: Every time.
With the exception of the TP thing (aka, doing something that has to be a bot, because a player can't do that), then there could be legit players that do that. I have very slight OCD. It is not noticible to anyone but me generally, and it is in a very small amount of very specific things. Like I have to count my fingers when I pop them, and I have to pop every finger at the knuckle if I do one at the knuckle, or all in the middle of my finger if I do one in the middle.
That being said, I know some seriously OCD people who have some really complex rituals with very specific timing. I guarantee you there are people who play / played D3 and did exactly what you are suggesting, with their own twist maybe, but that twist would be consistent too.