Possible Chance Cross With Sweet Ozark Orange

[friedgreen51]

I had been looking at a particularly healthy Sweet Ozark Orange tomato plant in my main garden that had several really nice tomatoes. It was healthier than most of the other OP plants. It ripened this week and much to my surprise it was red. I am really careful when I save seed so I don't think I mixed it up with another variety. I am also really careful when I plant seed completing the planting of one variety before I move on to the next. Could this be a chance cross, possibly with a hybrid such as Park's Whopper or Goliath, both I which I grew last year in the same general area of the Sweet Ozark Orange?
I had another Sweet Ozark Orange plant in another part of my yard closer to the house. It also produced a ripe tomato the same week. I planted both of these plants at the same time and they were both grown from the same seed that I saved from last year. I have attached a picture of the 2 tomatoes side by side. They are amazingly similar in size and shape. One is what I expected from a Sweet Ozark Orange and the other is the red surprise tomato. By the way I sliced the red one tonight and it was delicious. I saved the seed.
Any thoughts on this would be appreciated.
Deborah