How is it picking the comments?

If it's all comments, including flagged/dead/downvoted/etc., then it's not reflective of the actual filtering HN does.

But if it's weighting comments by their likelihood of being read -- e.g. mostly top comments on popular stories -- then I'd be a lot more curious.

I'm not surprised AI spam has increased substantially. But I'd be surprised if it's affected the comments most people actually read to anywhere close to the degree shown in this graph.