Although it was a hard decision for others, Atlan, found it to be the most logical course of action. Since he could hear the conversations of the Canzers, he knew that the Big Nose sneezing Canzer didn't plan its sneezes ahead of time. It showed no aggressiveness against the humans, at least for now.
However, the bearded Canzer named 'Gee' was actively trying to attack them. It was practically fuming. And now that it was permitted to attack, then Atlan did not doubt that it was only a matter of seconds until it did.
Compared to the sneezer, choosing to defend against the angry 'Gee' was a no-brainer.
Atlan was frustrated that they couldn't hear what he heard. He could have also told them about his ability to understand the Canzer's language, but that in and of itself would open a can of worms. Not to mention the fact that they might not even believe him, the trouble would come if they did.
Sorry for the unstable updates. Don’t have my current set up right now but will update at least two chaps a day