I have no idea. Try over on the Name That Plant! Forum.

Rodney

The leaves and plant growth looks much like petunia. Did you perhaps have petunias growing near that pot last year. Petunias will reseed so a stray seed might have dropped in the pot and germinated when the soil became moist

I second petunia. My petunias always reseed themselves. They look very much like your seedling.

Looks like a petunia.