Apparently this agreement was made a few months ago for Mysterio to leave at the end of February. Also, the AAA promotion in Mexico has scheduled a press conference for Tuesday
http://www.f4wonline.com/more/more-top-stories/96-wwe-news/41389-mysterio-no-longer-under-wwe-contract
http://www.f4wonline.com/more/more-top-stories/96-wwe-news/41389-mysterio-no-longer-under-wwe-contract