Who gives a shit what a level 6 should use crystals on? That's not your decision. You have no idea if they used crystals or not. Many, many times I've attacked twice in a row with no time between. The player may have used inventory troops. If you know what you're doing, two attacks in a row is easy. But, your post makes it pretty clear that you don't know what you're doing, so instead of learning the tricks better and more experienced players use, you'd rather assume that they were cheating.
And being a level 6 doesn't mean shit. They could well have a maxed out level 10 base and a level 6 on the side. And a max level 10 player can use a level 7 base to wipe level X's easily. As always, when you lose, it's probably just to a better player, not a cheater.