Yes, continuity error, or possibly that what Lex suspected was, like Stalker said, the Queen finding her way up.
But I don't see how that was possible, when:
a - She popped up somewhere else
b - The Queen was nowhere to be seen when they were going up the tunnel
c - Even if she WAS in that tunnel, she popped up AFTER they got up
Unless... Well, unless she started digging out somewhere else in the tunnel, but that's pulling at straws there.
"To me, everyone is crazy. The ones in the Mental House just got caught."