For there to be a violation there has to be a reasonable prospect of consumer confusion by the consumers in the target market. The page is labelled "Choose your WordPress Hosting plan"

Someone who is in the market for Wordpress hosting is almost certainly aware they have Wordpress and that they need hosting for it. Wordpress is a nominative use to refer to the entity, and Core is an adjective which in context means central.

Do you actually think there are meaningful numbers of people who have believed that WPEngine is actually wordpress itself? That would be the standard. Wordpress.com leads to much more confusion on a regular basis.