I've seen horses kept like this before, and IMO neglect is abuse. You KNOW when your animal looks skinny and unkept.
Still, we should not jump to conclusions in every case of a skinny horse. For instance, if you see a skinny horse in amongst a herd of ones in good flesh, it could be a hard keeper. And it DOES take a lot of time to fix, if indeed you can. I'm pretty sure that "Corporal" (1982-2009, RIP), who was a skinny 4yo when I beat out the Meat Market by paying $140.00 for him at auction (1986), had never been in good flesh. He never did fill out and get fat.