If he felt he didn't get done the things he wanted to do because he was constantly flitting around on a hundred projects, wouldn't you call that a procrastinator?

I would. I'm the same way. Most people wouldn't call me a procrastinator looking at my output, but I know how I feel.

It's hubris to claim to know how Leonardo felt, of course, unless he wrote it down himself, but I don't think the article's nearly as big a stretch as you think it is.