Notho eggs can skip diapause and hatch in water but I doubt this is what you are seeing. If you catch the fish I expect it will be an australe or gardneri that snuck into the tank as an egg on plants.

Hello,

I have water incubated Nothos. It takes about 3 weeks at 78oF. I used shallow water in a petri dish. Some peat came along so the water was slightly peaty (I picked the eggs out of peat I collected). Once I saw well formed eyes with a gold ring around the iris I hatched the eggs by adding them to a small container with several table spoons of freshly prepared peat.

I have seen N. korthausae hatch out spontaneously from being spawned into the gravel of a planted aquarium but all the fry that hatched this way were belly-sliders.