If you want to nitpick, I can point out that the full quote is "Europeans between about 500 and 1300 mostly couldn't paint"; stress on "about", and those aren't paintings.
Besides the comment started by saying that "medieval European art generally sucked", so it covers the work I mention.
That's if you want to nitpick. If you don't, both those works are hallmarks of medieval art and while they're not necessarily exemplars, it is important to remember that there were still artists who knew their stuff in and out in medieval times and the Renaissance didn't come out of nowhere.
Edit: I travel through Europe by train a lot (mainly France and Italy but also Switzerland and Germany occasionally) and I visit museums, cathedrals, and art galleries in every city I stay. I have seen a lot of medieval art because those places just seem to have it lying around by the bucketload. There is a broad range in quality, but I have seen some very high quality woodcuts and, indeed, paintings, although those tend to be religious icons. Sculptures also, but mainly in statues of saints on the outside of cathedrals (see e.g. the Rouen cathedral). I'm trying to say that I'm not some kind of art authority or expert on medieval art, but I have seen my fair share of it, and no, Europeans didn't just suck at art in the medieval. I think what happened is there was a lot of mostly religious art that was lower quality, sort of like you can find plenty of slop on the internet today, but there were still skilled artists that created shockingly good art. You'd be more likely to find it in the palaces of the rich and powerful, I reckon, because they were the ones who could afford/support talented artists, as opposed to more ordinary craftsmen, who would be paid less. For the same reason you might find less of the good art lying around than the rougher, cruder kind, because the former was more expensive and thus harder to obtain. This also goes for religious art, which tended to include a smorgasboard of art forms, from painted icons and sculptures to reliquaries and liturgical equipment like communion chalices. But good medieval art existed, I've seen it, and it wasn't that rare.
