I've fed my eldest on cocobark, eco earth and shredded paper over the years. He's also my fussiest one where he will usually refuse FT and just eat live.
Never had a problem. He's over 20 now. My current batch of noodles are all on ecoearth/cocobark. No problems there either.
EcoEarth is so fine that you shouldn't have a problem if they eat a little bit. Yes, it cannot be digested, but it's not a lot of it with how often they eat and all. If you have them on repti-bark or the larger wood chips and they swallow a larger chunk then that could potentially be an issue, so just make sure to use the smaller wood chips.
It sounds like a wood mite or if he'd fed live, it could have been a rodent mite. Reptile mites are small black little ones by the time they're able to be seen with the human eye.
Oh Thank you so much! This puts me at ease. I love my baby and I just wanna make sure he's safe. I feel like he's a happy noodle, but I'm also a worry wart. lol. That definitely eases my mind quite a bit. Thank you!!