I have talked with (and played against) the majority of the people who play Multiplayer. Not every player who has ever played, but the vast majority who have played more than a few games. Aside from Prussian and myself, I have confirmed through conversation 1 other person who has 100 multiplayer wins. Even the mighty Eck doesn't claim to have that achievement yet. If I were to guess, the total number is less than 15. If it was more then, there is a facet of multiplayer going on that I didn't know about. While that's possible, I find it very unlikely.
Steam leaked the number of players that owned Battletech a few months back. It was under 190K players. Add in Paradox and COG and we'll give a generous estimate of 250K players.
Lets high ball the number of players who have 100 multiplayer wins at 50.
That's 0.0002%
It's not bugged. Steam just doesn't show that many zeros.