Push notifications getting through restricted networks?

Last week I was on a cruise where satellite internet was available at ridiculous prices. Internet was sold by minute, and you had to login with your stateroom information after connecting to the ship's WiFi network to get access to the outside internet.

However, I noticed an interesting pattern with my android phone; When connected to the ship's WiFi, but without being logged in or using any internet plan, I would receive push notifications! (they were not local from apps on the phone, It was for things like instagram and pushbullet updates)

How were these push notifications getting through the block, while normal internet traffic was restricted? I tried HTTP, as well as SSH and never could connect unless I paid for the plan.