Some wikis are set so that whenever a new user makes a contribution they get some version of that message posted to their message wall (not my favorite thing TBH, I prefer the older talk page system myself but whatever). Sorry to disappoint you, it's just a bot.
I posted that reply in all caps and acted as if I "really appreciated it" because I felt like it. If I were to actually be serious, I would of typed something like this: "Thanks! I really appreciate it!"