We probably will never know. I have tried to validate this story having additional admin information about the user but it has not lead to anything.
The few items to reason that the post may be real could be:
1. The person did not seem to be making a big deal out of the 2 admits, though you can imagine just posting something like this in a low-key way is a big deal
2. It is not uncommon for people to be surprised with their applications they did not care about - something shows in Interviews or in the application where the school senses that the person does not care to persuade them, and this confidence is something schools cannot resist reaching out to.
3. The person is probably not a typical candidate from their industry/background (but this is simply based on the email address interpretation)
Just some other food for thoughts.
P.S. It seems also odd that they would be rejected from Smith and Anderson but admitted to GSB and HBS...