As far as I can tell, they're the only MM that lists SOLI as a security they are trading.
Even if you take out the CDEL part, the rest of the post stands. It seems like a reasonable conclusion that CDEL is the sponsoring MM, especially given that they have several other Expert Tier securities. It appears they take on riskier stocks in general.
I haven't looked at every MM. If you find another one that lists SOLI, feel free to post it and I'll reconsider CDEL as the sponsoring MM.