Frightening Vendini, inc Data Breach Notice

I received this notice today about a data breach from Vendini, inc. It's extremely unhelpful given that I have never explicitly interacted with Vendini but rather a company that uses their service. Basically there is no way for me to know what information they may have since I don't know how they obtain my info. My concern is that a password or username I use elsewhere was compromised... but I don't know what if any that might be.

Has anyone else encountered a situation like this? I haven't gotten notice from the venue site that I used (not sure which it is)... what is their responsibility?