What you are probably confusing is that the mobile networks (LTE/4G, 3G etc) and some of the WISPs cannot obtain sufficient IPv4 addresses for everyone to have a direct public IP on the internet. (as you have on an ADSL, FTTC, Cable connection today).
So they use what is known as "carrier grade NAT" (CGNAT) which shares a public IP address with a lot of users.
This means unsolicited incoming traffic to you hits the CGNAT and cannot determine which user to pass the traffic to, thus showing "stealthed".
GRC was good in 1999 / 2000 when high speed internet in the US was a single PC connected to a cable modem, and no home router. The UK has always been different. The GRC site hasn't really been updated, so much of its advice is just aging gracefully. Not wrong, but not always directly applicable.
plusnet unlimited fibre
80/20 - Since 2 Jun 14 - Aug 15 Sync: 56575/9911 - G.INP download only
16 years UK broadband (Since 1999 ntl:cable trial), Asus RT-AC68U & HG612 - BQM - Flash Speedtest - HTML Speedtest