This is still a very controversial statement, and far from definitively proven. Yes, even with a nature paper.
I also take issues with the phrase "lots". So far this effect has been observed only locally.
I believe the result, and I think it needs broader investigation but a summary like "gene-editing causes lots of mutations" is not accurate.
You may be interested in my comment from the last time this journal article was posted to HN.
It should be noted that "controversial" scientifically means something different than in the general public. What I mean is that we see and believe the current observations but are still waiting to fully understand the extent and reproducibility.
I'm also a biologist.
I guess I don't understand where your concern arises. I and others I know have used CRISPR-Cas9 to introduce arbitrary DNA mutations at loci of interest. We see many different types of lesions, ranging in size.
But anyway, I was just relating what I've heard from colleagues and my dis-taste for the articles definitive title.
This is why it is controversial.
I am taking issue with the articles title "CRISPR-Cas9 gene editing causes lots of mutations"
From the current literature, there have been bad and good examples of this, but it is still a field in flux. We do not know conclusively what the effect is, how large, and how local. This makes blanket statements like "CRISPR-Cas9 gene editing causes lots of mutations" controversial.