Honestly, a quick change in diet, can cause that. when I saw what you were talking about, I was a lot less concerned, then thinking poop runs that sprays everywhere.
Yes, those are looser - I would deworm, too. Goats can get worms, which can cause looser stools. Since you are doing a fecal, it won't hurt to do probiotics and wait to see if there's worms.
Bloat issues, can also cause looser stools... and so can eating things they shouldn't be eating.
Over-eating can also cause the stool I saw.
If you over-eat, did you know that you'll end up having the runs because your body can't digest that much at once? I would consider muzzling him and seeing if reducing his free-range ability fixes the problem.