Hu Dagao was the tenth heir of the Hu clan and thus had access to a lot of information that most people could only ever dream off.
He even knew about the various concepts that were related to the space as well as the existence of the different layers of the Void. This also included information of how Teleportation arrays and such worked.
Of course, this was all just theoretical information and wasn't the same as being able to use it.
But just this awareness alone was something extremely rare in the Ming Dao world. It could be said that Hu Dagao was on the same level as Ji Shirong if one considered their knowledge base, with Shirong exceeding by a little due to his interactions with Lin Wu.
As such, Hu Dagao realized what Lin Wu was doing in front of him.