I don't think you read the article
What WP Engine gives you is not WordPress, it’s something that they’ve chopped up, hacked, butchered to look like WordPress, but actually they’re giving you a cheap knock-off and charging you more for it.
Which is a more serious allegation, and trademark law would prevent them from calling it WordPress if they modified the software. It's pretty common in the open source community to insist forks use another name to prevent confusion.