I have planted tomato seeds and as far I remember I didn't put more than one seed in a planting hole of each seedling container. I was using tweezer to drop each seed into a hole. However, I am observing in 2 of 10 seedlings that I seeded two growths from one seed. Is it possible or I might incidentally dropped two seeds in a hole in those seedling containers?
Yes, multiple tomato plants can sometimes come from one seed. I've grown a lot of tomatoes, but I've never seen it happen for sure myself. I've heard of it happening.
They call these polyembryonic tomatoes.
Here's a link that talks about some polyembryonic tomatoes that were found: https://cdnsciencepub.com/doi/abs/10.4141/cjps58-010