Yeah, but in what form were the argon species? Excited states. This is a ground state argon compound. Pretty cool.
As for the question about stability, you need to remember that we're dealing with professors who will own you for saying something about 'stability'. Thinking about it in terms of stability is probably perfectly fine through HS and even most of college. The problem comes when someone asks you 'What's more stable?' If you think about it, it's really that the compound is more reactive. Then you get back into the electron count, etc. However, there are also compounds that are thermodynamically unfavorable, but can still be made. It just depends on how much energy you can put in and in what manner. Take a look at cubane. Thermodynamically, it is extremely unfavorable (you've got to put a lot of work into making it). Kinetically, it's solid as a rock. This is how many of these noble gas compounds are made: although it is thermodynamically unfavored, they add the necessary energy by blasting it with UV light or fast electrons, and then new molecules form, which have a kinetic barrier to dissociation.