No tumors or stones is GREAT news. And the kindeys looking good is also great news. I must admit though, I would wonder why these crystals did not show up on the last urinalysis.
Now, your best defence is to make sure Luna stays on the correct food. (I hope they let you know what type of crystals they found).
Biddy is having this crystal problem right now, and the food is not doing enough for him. (but that is another story)

Now Luna and you can get a good rest, and hopefully the results will come back with good news as well.