They changed the brand name because they thought having the term "mix" may scare bitcointalk users and will not encourage the users to use their exchange. Although I told them it's not a problem because they are not a mixer. But they thought to stay regulated with the community standard. So they decided to change the term from "mix" to "mex". There were no other reason for changing the brand name.
I know that, but no business that have word MIX in it's name should change it if they are not mixing coins (not allowed by forum rules).
If you remember there was another service with MIX called Mixin Safe, that was not related with any mixers.
There is also Mixcloud music streaming service, there are mixtapes, and other words with MIX that are not affected by new rules.