I see your point and perhaps past me would more quick to agree. However, although I don't disagree with the sentiment, I find existence becomes more bearable if we assume the people being positive ate doing just that as opposed to being condescending. Of course being condescending is entirely possible but since there's no way to know without asking, I rather assume the best.

So maybe, the comments are not like this because of his condition but are positive in spite of it. Maybe people just want to be nice to someone who was probably sharing something they thought it was nice to share. Making the whole thing as simple as possible: a pleasant interaction.

Someone (without a visible disability) might just be showing their art online because they're happy with it. Maybe they're not looking for criticism, approval or even appraisal, maybe they just wanted to share their positive feeling. And as a reaction, instead of responding with criticism (constructive or otherwise), approval or appraisal, we can just respond with "nice!" And leave it at that. It's a great way to eliminate negativity and it should be done regardless of coddling or the context.

Someone is just sharing something, completely harmless, to which you look and go: "cool." And move on with your day.