I doubt it.
I mean, I'm not completely denying the existence of new fruit, but I don't think that's a hint of that. I think it was SwitchForce who spoke about it and also about the flavors in the vending machines (another thing I don't really means anything).
I'm conflicted about this idea of more fruit being in the game. On the one hand, I feel like it's something relevant enough for Nintendo to show in the Direct, but didn't. However, it also makes me think that maybe Nintendo wants us to explore more about the additional content hidden from what we've seen. In which case I feel there's more to what we've seen in the Mysterious Islands. Likewise, Nintendo was clever enough to only show us the savory tab of the recipes we can cook, so maybe they're hiding the desserts because we might need additional fruit that they've purposely didn't show (like maybe a banana bread or lemon pie?).
But again, I want to keep my expectations low and I'm honestly happy with what we have. It could also be the case that we might not need additional fruit for recipes. Maybe they'll keep all desserts/sweet things limited to the fruit we have.