I’m confused, in the article he said it was a brick to whoever has his stolen phone. How did they get his phone number to send him text messages? Did they crack the passcode and needed the iCloud password?
I think when you remotely wipe the phone you can make it show a message with your phone number, in case you're actually a honest person that found the phone instead of a thief.
Typically if you report the phone stolen to your provider they blacklist the IMEI which gets shared with other providers so the phone can no longer be used. I was unclear on this part but a new e-sim can be provided for the new phone, and the old sim banned or the old one transferred. Regardless, the old phone will still show the IMEI/sim/phone number, which is how they got that to text them
They almost definitely got this info by simply having the IMEI, which is printed on the back and can definitely be accessed in whatever Apple calls their service mode though.