That's not an official specification of any kind, and that statement doesn't get approved by any third parties (a problem which has plagued the abundance of the term "natural" for years). In order to make this transition, a spokesperson said that General Mills will be sourcing different cornstarch and sugar, which presumably accounted for the majority of genetically modified components in the original recipe.
Right now, there is not much scientific evidence to show that GMOs are harmful; however, the concern generally seems to be that there could be long-term effects that are, as yet, unknown. It definitely seems like General Mills is giving consumers what they want, though. We'd argue that a next (and perhaps more effective) step, in this case, would be to make a commitment to wholly organic ingredients and sustainable farming practices. The blessing and the curse there, of course, is that those things are a lot harder — and a lot more expensive — to pull off. (USA Today)