I operate a site of the form brand-widgets.tld and recently I noticed a lot of 404s appearing in GWT. When I investigated the source of the 404s I discovered that they were all for pages that never existed on my site. Moreover, they all were listed as "linked from" different-name-widget.tld
When I visited different-name-widget.tld I discovered that it 301 redirected to my site. In fact, it didn't just 301 redirect to my home page, but it redirected to an internal page. Namely,
different-name-widget.tld/ >> brand-widgets.tld/category/ (301 redirect)
different-name-widget.tld/random-page.php >> brand-widgets.tld/category/random-page.php (301 redirect)
So, the base url of the other domain is being 301 redirected to a category page of my site. This also explains all the 404s in GWT because those pages may once have existed on the other domain but obviously don't exist on my site.
Even after figuring out all this, I thought it was possible this might have been done by mistake, but then searching around, I found that there were quite a few recent spam links to different-name-widget.tld (more recent than the first 404 error from the redirect in GWT).
Going back to GWT, I found that a couple of these spam links are appearing in my list of backlinks with the "via this intermediate link" note (and the intermediate link is different-name-widgets.tld). Not all of the spam links have appeared in GWT tools as yet.
Anyway, I'm a bit worried now. I am fairly sure this an attempt at negative SEO (though I have no idea why, the niche is not competitive). Should I use the disavow tool preemptively and add in different-name-widget.tld as well as all the spam links pointing to it that I can find? Is there anything else I can should/do?
I would appreciate any help/advice. Thanks!