Cho’Gall can only be selected when you have two picks available in the same round. Since you both could not lock in Cho’gall, and you didn’t have another double pick round available, he is no longer a valid Hero selection.
Additionally, if you are hovering or pre-selecting a Hero that is not available to be locked in (for example in this case or if they are banned or already selected) when the timer runs out, the draft is ended and leaver penalties are given.