I'm guessing they mean rather than build a static Next site that generates 10k+ pages (or whatever large means in the given context), it instead creates one page that just queries the data from the client.

I have one Next static site that has about 20k pages and takes about 20 minutes to build and deploy. I think that's an acceptable build time. But I do know of other people around the net who have mentioned having sites with 20k-ish pages taking an hour+ to build. For them I could see the desire to try this sqlite trick.