Probably because the account was used as collateral.
As discussed via pm.
-----BEGIN BITCOIN SIGNED MESSAGE-----
Date: 13/03/2015, Friday
This is validium and am in control of this address and am requesting a loan of 0.3 btc from Muhammed Zakir. To be repaid within a week and a half using my account as collateral
-----BEGIN SIGNATURE-----
15LUmGvPLTM3pHMw7qBj7yhjnMhbD9JFKH
H7up/sdhQvFw09nZ2rnN6at13LInHVEYPN95/epfi5EBNtQr/SWr59PeUM9jenHzHSS9kk3Pg50dZFw1OiBmmFw=
-----END BITCOIN SIGNED MESSAGE-----
Exactly, Zakir even addresses this in the thread:
P.S. Can I change address of your account so you can cover some of the loans with Bitmixer payment?
If the loan was from ~a year ago, and the duration of the loan was for >a year, then I think it would probably be fair to say that the borrower defaulted on the loan and that MZ became the owner of the account, in effect making that account an alt of MZ