Aquariums: Potential killifish eggs in store bought sand?

So I recently set up a 10 gallon to hatch some Pygmy Cory eggs from my main tank. I was able to get two of them before fish ate the other eggs. I hatched these eggs in a net inside the new tank. Only two fish hatched from them and are definitely Pygmy Cory fry (first picture). However, I now have 3 mystery fry that are in this newly set up tank that have no possible way of being there (2nd picture). No other eggs were transferred into the tank from my main tank and they are obviously different species. Wondering if they are somehow killifish eggs that were dried up in the sand I bought? Other fish in my main tank are CPDs and Cardinals.