Poor Hudson....almost retired...
I still think the only explanation is the Queen but even that is grasping at straws as we don't know for sure if a Queen can lay an egg without her sac or even grow a new one. AVP extinction did do that but it was merely a game mechanic for a game that isn't likely to be canon.
The Queen could have had the egg on her back...maybe.
Another explanation is A;CM and yes I know how terrible it was but in that game, the xenomorphs were brought on board the Sulaco by the Legato.