A meaty question

Can anybody tell me how this happens? I bought some hamburger meat and didn't open it until a couple of days later. It smelled OK, but when I started breaking it apart this is what I found:

While the outside was all red and pretty, the inside was brown and slimy!! YUUUUUCK!  The only way I can think this might happen is if they wrapped new meat around older meat to get it sold. G.R.O.S.S.!!!

Unfortunately I'd thrown the receipt away already so had no proof of when I purchased it and the manager at the store told me that there was nothing she could do about it. Needless to say I'll not be shopping at that store anymore.