Welcome to the forums Nick!
Sounds like an interesting experiment. You might as well try to take care of the odd one, and see what it turns out to be (remember to come back here and tell us!). I don't know much about the science of triploids, so I am afraid I can't help you there.
Anyway, this seedling is from an unknown variety of apple. About the size of a large Cortland, taste sort of like a McIntosh, bright crimson skin with large streaks of russett, and purple flesh for about 1/2 inch below the skin. If you have an idea of what type of apple this is, please let me know.
Hmm.. You are in Maine, wish you could bring some of the samples to the HOS Apple ID team. They do a great job figuring out what variety an apple is. Purple flesh sounds interesting.