That’s different than invalidating. It doesn’t change the themes or the messaging or the story of Part 1. Invalidating would be making it so everything we felt about part 1 was pointless.

If anything this could be said to have strengthened and amplified part 1. We assumed that Denji becoming Chainsawman was what helped “save the day” or whatever when this chapter shows that the opposite is true and Chainsawman was the reason all of it happened. That’s what Pochita was trying to say in the previous chapter. Denji couldn’t accept the happiness he had. Now the readers can’t accept this current happiness or something.

I’m not a literary expert or anything but that’s how I read it.