Sorry i haven't responded to your question but its becase the binary has a SUID bit meaning if we run the binary as a different user it will still be running as the user who has the SUID bit set as

Example if a root's binary has a SUID bit it means that even if we are not root and we run the binary, we are running the binary as root and not as our user. In simple term SUID bit gives us the permision of the user the binary is belonging to