Your IP address tells MN (if they bother to check) which ISP you belong to. It can allow them to see that the same IP that posted in chat also posted in AIBU so they can be 99% sure it's the same poster.
Now some peoples IPs (dynamic) change everytime they turn on their PC.
If you use a router it probably changes once a month or when you turn the router off and on again.
Some people have unchanging (static) IP numbers, but you generally have to ask for one especially so if you don't know then you probably don't have one.