That's the real 5G.
AT&T labels the LTE-Advanced fake 5G as "5G-E", with a very small "E" subscript after the "5G". You don't have that, so you're getting the real thing.
On all my Samsungs (S8, S9, and current S20 FE), LTE is shown as "4G LTE". On my old BlackBerry Z10, it showed just "LTE". When the Z10 dropped out of LTE, it would show just "4G", which is really HSPA+, or 3G Advanced.
My wife and I both recently upgraded to 5G phones, my S20 FE, and she got the iPhone 12 Mini. Unfortunately we never changed our actual plan, so we both still get just LTE, and the occasional 5G-E if we ever drive in certain parts of town. We'll get around to updating our plan eventually. Or maybe AT&T will change it for us. It seems that's what they did for you.