Where is it documented Automattic (or Mr Mullenweg) owns any of WP Engine?
(ETA: Not saying it's impossible he or they have an interest -- I've just never seen this suggested. WP Engine is in many ways a competitor to wordpress.com, so it would be unusual, I think. And he/they have long not been a fan of WP Engine.)
2018 would tie in with about when I first got the impression he was not a fan of WP Engine. I'm sure there was fuss once before (about them not being on the "recommended hosting" page?)
(ETA: Not saying it's impossible he or they have an interest -- I've just never seen this suggested. WP Engine is in many ways a competitor to wordpress.com, so it would be unusual, I think. And he/they have long not been a fan of WP Engine.)