If you do not see the striping, which for the most part is a recessive trait and should be "locked", then could be a cross or more likely an errant seed/plant mix up.

There should be some evidence that it's been crossed because the striping trait is not completely recessive. Careful inspection of the skin in good light will show faint or partial striping. This would indicate that the genes are heterozygous which would mean it crossed last year.

I would not assume it is a mutation. People assume mutations over "mistakes" far too often. Seed mistakes or plant switches (human errors) are far more common.

Thanks! It looks very, very similar to a couple other bicolors that I'm growing so operator error is likely the cause. I always thought I was pretty careful with my labels but I guess I need to be even more careful.

even when you are very careful, stuff happens