The uncle is well, weird.
Considering his past, it's pretty understandable that he's gonna hate MC, and we've also shown a glimpse of his hatred in this chapter.
But he's also the one that sheltered MC, and according to MC, unlike the other family, uncle doesn't show contempt to MC and mostly left him to his own device.
Maybe MC stealing his wish was the final straw, but then his previous indifference doesn't really make sense.
Maybe it's connected to the "dog" appearance? I mean, he just saw some "thing" taking the visage of your deceased beloved after all, that's a lot of mental damage.
How did the "dog" connected to everything anyway? By the reaction when the uncle saw Chiyo, it seems like the "dog" ain't connected to the ritual to summon Chiyo, so did he perform 2 separates ritual simultaneously right before he collapsed or something?