You'll come to find that the people who work at petsmart are idiots. They read a couple books on how Petsmart thinks fish should be cared for and then go to work. If I were you I would report that employee because he/she went against Petsmart recommendation on that one.
Never keep male and female bettas together. They may seem fine now but I guarantee you in time you'll end up with a dead fish.
Also.. 1 gallon is not big enough for even 1 betta, let alone two. Separate them and try to get them each into a 2 gallon or larger tank.