Can someone explain exactly how Facebook hacked and intercepted a text message?

I have an Android phone (Blackberry KEY2). I do not have the Facebook app installed on it. I did log onto Facebook once on it via the Chrome browser to confirm it worked.

The other day, I responded to my granddaughter’s request for a video chat via Facebook for kids using my laptop. Apparently, all the kids her age (5 yrs old) are chatting with each other because of staying at home because of coronavirus. While in messenger, I briefly noticed a text message from a friend whip by. It was probably on the Facebook page (I didn’t have anything else open and video chat was smaller than the other page, overlapping a good part of it).

After the video session, I couldn’t find the text message anywhere. I emailed him back and he said he did not send it over Facebook, he just sent a text from his cell phone. I checked my phone, and yes it was there as an unread text message.

I am now perplexed, I never associated my cell phone number with anything in Facebook. I hardly ever use Facebook. So how would Facebook know to intercept a SMS message and display it via my Facebook page on my laptop?

What’s more, I don’t have any other app on my laptop that is aware of my cell phone number, especially anything that was running.

I went through my profile on Facebook, and my cell number does not show up in it at all.

It looks to me like Facebook has somehow, surreptitiously associated my cell phone with my account. Is anyone else aware of anything like this? How do I get my cell phone number disassociated? If I do not use the Facebook app, what other data could Facebook steal from any device (phone or computer) via a browser? Or, could anyone point to where text messages are supposed to be found within Facebook via a browser?