I canceled the phone line AT&T created for my old apple watch - was that a mistake?

I have been an apple watch user for ~5 years. My original watch had cellular and GPS, and when I activated it, I created a line on my AT&T account with its own phone number for this watch. I was told this was just the way it's done to establish cellular, but my watch would totally mirror my existing iphone, and I wouldn't even need to know this phone number. ~6months ago I replaced my watch with a series 9, GPS only.

The other day I noticed there is still this dummy phone # on my cell phone bill from AT&T (half my relatives are on my account so I did not notice this right away lol). I realized I never canceled the phone line. After triple-checking that it was the phone number going to my old apple watch, I canceled it.

My watch still seems to be working like normal (I even tested it answering calls on it just now) but I got a couple of scary warning messages from AT&T saying I will lose functionality if I cancel this line.

So my question is: Does my non-cellular apple watch still need to be on my AT&T account?

Sorry if this is a dumb question! I was on a chat line with AT&T for 1hr+ the other night, and customer service really has no idea how any of this works.