What's the correct ruling?

[RocketManJames]

Late night at the local B&M.

Guy looks down at his 2 cards... he realizes he's been dealt 3 cards. He immediately tells the dealer. No action has taken place yet.

What is the correct ruling?

What the floorman did definitely made sense. What's the correct way to handle this situation? I've seen the 3-card problem before, but this is the first time it was handled this way, and it certainly made sense.

-RMJ