He really wasn't. The video's already been posted of him immediately standing right back up with perfect balance and continuing just fine. Even Masvidal recognized that. He himself said he didn't attack not because he was gassed but because he feared Colby would take him down if he advanced. He thought Colby was fine too.
Being hurt is when you're actually floored and can't get back up, when you turtle, or when you start stumbling all over the place. Colby did none of that. Flash knocked down and that's it.
Hence why Colby still won the round despite being knocked down as it really wasn't anything special.