The bonus at the right send player back after 0.3 seconds, which is enough to click another button(next to), and 2 wool got.

This is against the rules as the exposition button in the Freebie room specifically states "You may only take ONE freebie wool".

I'd just treat it as an exploit. "But just to warn you, you may only choose one. If you select a colour, this room will become inaccessible." means the "only choose one" is done by the map, not the rule.

The wording is still pretty specific, enough so to consider this matter closed.

specific to which way?

"You may only choose one", specifically states we can't take multiple. We can not just ignore those words simply because of the possibly context change. In those statements, it's a separate sentence, and therefore thought, from the next one stating that the door closes behind you. You may only take 1 freebie.

http://www.dictionary.com/browse/warn warn is only giving an advice, not limiting your behave

http://www.dictionary.com/browse/may may can be used to express possibility

We aren't here to pick on fine details. The matter is closed.

We are analyzing the sentence ^_^