Yep, you nailed it. A lot of the SEO-related articles, videos, blogs, and whatnot out there are saying that anchor text diversity is a must because it makes you look a lot more natural. They could have thought of something that would catch those who are using the same anchor text over and over again, and treat them as if they're using some sort of a submitter software, or something.
Anyway, about directory submissions, all I can say is that you shouldn't blast 'em. I've heard some people using software to blast their links on directory sites, or even having a group of people work on submitting just one site to a lot of directories. Just... don't do that.