Yes the rules for access to the DC lounges are often less than clear.
Since they are using the Aeromexico Salon Premier lounges in Mexico, do you think that they mean " Flights on Mexican(a) Airlines (regular and low cost) are not accepted " ?
I shall be travelling through MEX in a couple of weeks (flying on Mexicana to EZE), and will try to access one of the Salon Premier lounges using my DC card. I will post the results.