My thought is that the races have known each other a while, maybe pretty close to year zero.  In fact, year zero, then 100 years later when the galaxy then imploded drew the attention of Cassi's race.<br/><br/>They jump out there and meet the Hydrans.  In fact, in an exchange of knowledge, the two races agreed to help the other out.  Hydrans finding their destroyer, Cassi's race safe guarding their water.<br/><br/>Thats all I got so far.