they are not selling user data

they are not collecting user data on ubuntu servers and selling it.

they are selling page impressions (advertising)

yes, the act of rendering the page tells the servers that are being queried what you are looking for, and your IP address because that's the way the Internet works (it may also send a cookie if you leave them enabled, which may let them correlate your queries more precisely than they could just with the IP). it's not clear at this point that your IP address can/should be considered private information.

selling access to your eyeballs is something _very_ different from gathering your personal info and selling that.