Pressure in new tank- found out why

So I had a new gas Tank and sending unit installed on my 67 Barracuda about a week ago by a trusted dude that I use a lot.
Anyway I went to fill up today and noticed pressure when I released the cap.
Upon investigating, I found a Port on the new Sending Unit cover plate that is NOW tied into my filler tube vent with a new rubber hose. Before I ask my guy why, I wanted to check with ya'll and ask ... Is this normal? I mean there IS a port there. I know for a fact the old tank does not have this and vent WAS open to atmosphere.
BTW Its a 360LA crate motor and is running fantastic since new tank ( 150 miles)
Just concerned about pressure and new set up. Trying to learn.
Thanks