I highly doubt that your crested goes grocery shopping for gecko-pies at night...
You say you are certain that there were no crickets in the enclosure, but can you be abosultely certain? They can hide almost anywhere!!
They are bounc to ingest a little substrate when they have a miss, or grab some dirt with the cricket. As long as you are using an appropriate substrate, the consumption of a tiny bit of it should be fine. If you get worried, then you should be checking for poops, because if they get their digestive tract clogged with substrate, then they will become constipated and will not be able to poop. If you get really worried about it, then you could always change the substrate to something that he cannot ingest, such as newsprint or paper towel. The disadvantage of these are that they don't hold moisture well, and crickets will often hide under them.
When one of my guys gets too much coco fibre in their mouth, they will often try to rub it off on a branch or the wall of the enclosure. I do believe that they realise it's not food.
If you have any more questions, feel free to ask!
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Amanda Heaton
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