Maybe he saw something moving and thought it was a prey item? I've not read anything like this before, but I've only read heavily about CG for about 2 months.
Typically people will recommend to use paper towels for the first week just to make sure the gecko is going to the bathroom. After that you can use whatever fits them and what you like.
Personally, if two are male and one is female, I would separate all of them until you're ready to dig through the substrate for eggs. I've heard that males that are raised together can do fine living together, but I would assume once a female is introduced things will change.
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