Frozen Hamburger Problem

I’m trying to cook a frozen hamburger in my air fryer. It says the internap temp is 60 on the box. When I was done fixing it, I took it out and it looked fully cooked and maybe a tad bit too hard. Before I took it out, the internal temp reached 160 on the outer edges but other areas were like in the 50s and 40s. And even 59 but it wouldn’t budge to 160. It was cooked 6 minutes on each side for 12 minutes. There were no specific air fryer instructions so I had to just guess.

I guess my question is… how did my burger turn out cooked even though the numbers weren’t all 160.

I just don’t feel confident measuring the internal temperature. How do I know when it’s done other than just looking at it? Do the numbers have to be exact???