Is it possible for server to send a wrong message to client?

So i got DC'd because of servers problems but after some tries i got DC'd again but saying "another person has logged into your account"

Im pretty sure i have not been hacked so maybe its a thing of my router or servers?

If you mean that the game locked the account and prompted you to enter a code saying someone other than you tried to access the account then it sounds like your IP address changed.
I dose not necessarily mean you were hacked but that the IP address of the last login attempt is different from the previous one...usually happens with some ISP's that change IP addresses daily

Nope it did not ask me for a code like when i change to another location. It just poped up to login screen saying (left bottom corner):

another person has logged into your account
Disconected


But i could log in no problems afterwards. Still scary message

I suppose it would depend on how quickly you hit the login button after the DC, actually getting disconnected from the server is not instant, it can take upto 6 seconds or more depending on latency and what was happening before, which is why you see quite a few qq posts about getting killed when they try to alt f4, logout macro...it's also why you see in other games a 10 second window to logout