By the 90s, 20” was considered small in the US. You can see this on the graph, by the mid-90s 27” was the most common size sold while sales of 20” and smaller screens were declining. Everyone I grew up with in the 90s had 27” TVs in the living room, I think this was fairly typical.
Computer monitors are much higher quality than TVs. Computer monitors had to display at least 640x480 progressive (at least by the 90s). This puts the TVL for a monitor at around 500, while 300 TVL was more typical for a TV.
And yeah, it’s possible for a small PVM to have almost no scanlines. A 9” PVM with 250 TVL won’t show scanlines. So it’s possible that the “what they actually looked like” pic is from a PVM, sure.
Brainbin posted a shot a while back that nicely illustrated the relationship between screen size, TVL and scanlines.
Basically:
small BVM = medium PVM = large Wega.