That was most likely an illegal distribution of the game. Sometimes people make copies of a game and then sell them (generally at a price way cheaper than a genuine copy). Even today you can find illegal copies of games, movies, etc being sold in stores can be found fairly openly in pretty much any major city, if you know where to look. As a bonus, they usually come with extremely broken engrish subtitles.

Fun fact: it is almost impossible to obtain a copy of JJ2 legally. The terms of use (license.txt) state you cannot "distribute copies of the Software by sale or
other transfer of ownership" and that you can't "rent, lease, or lend the Software". In other words, you're not allowed to sell it or even lend it to somebody. So, unless you bought the game off a shelf in 1998 or 1999, or managed to obtain an unopened mind-condition boxed copy sometime after that date, your copy of the game is illegitimate. For those of you that are concerned about this, you should delete your copy of the game and turn yourself in to the authorities immediately. This also applies to those of you who originally installed the game on one computer, and then copied it over to another, newer one.

Extra fun fact: The license also prohibits reverse engineering the game, and states this part in all caps. That means JJ2+ is so illegal that its illegality cannot be expressed in lower case letters. While it is probably ok to use JJ2+, its creator is almost certainly an international criminal, and will face justice as soon as INTERPOL manages to track down his location.