This glitch was first discovered in 2007 when hacking was at a height. It was only discovered because a hacker broke (filled) rooms 92-99, when you tried to join any of those rooms it would put you in the next room, but the next room was full so it would go through a cycle until it put you in the only unfilled room, which would be room 100. This could also be accomplished by filling room 99 and then joining it. Room 100 was just like any other room, nothing different about it. The glitch was that you weren't supposed to be there. This glitch can no longer be done because of recent updates that send you back to the room you came if the room you tried to join is full.
Understanding what happenedEdit
This is just a glitch. Gene did not open Room 100 up but it is a glitch that helped players to play the game even if hacking is at massive height. The opening of Room 100 is merely a life saver. However, it cannot occur ever again after the glitch was patched and found later by several players.