It’d have to be a little more complicated than that. Each lottery ticket has a unique serial number and, yes, they know which ones are winners.
Duplicating a winning ticket with the correct serial number and buying the non-winning one with that same serial number at the proper store would be more remote than actually hitting the thing by chance.
The odds of two big winning tickets even at the same store is astronomical. They are beating the system somehow. I have zero doubt.