I went to join the freeroll poker and i got a popup saying someone with the same ip was already registered. oh golly, fingerblasting incoming me thought, sarcastically ofc because im not a part of the herd of sheep that believes things for no reason at all

I asked why that could happen?
Do you use a free VPN?
As far as I know, VPN premium usually has a safe IP or at least the IP you use will not be used by others.
Why don't you choose to use the mirror stake site?
Free VPN can be of the possible reasons, the other possible reason is that he uses public wifi network such as in a cafe, office or other public places with free wifi which is also being used by other to access stake and play poker before.
What he can do maybe to ask stake which username/player who use the same IP, maybe he familiar with the username if the player is one of his roommate or maybe his own neighbor.
Btw, why he should use mirror site? Afaik it wont change anything once the IP is used by other then he will get the same message although he use mirror sites/links.