https://techcrunch.com/2019/01/14/sling-tv-rolls-out-free-content-to-non-subscribers-initially-on-roku/

Last year, Dish-owned streaming service Sling TV launched a free tier to its service designed to attract those with lapsed subscriptions to come back and watch. On Roku devices, former customers were able to tune into over 100 hours of TV shows and movies without a subscription by launching the Sling TV app. Today, the service is extending a similar offer to newcomers. On Roku devices, those who have never signed up for the streaming TV service will have the chance to browse and watch free shows, without the need for a subscription.

In other words, this is not a “free trial,” it’s a free – if limited – selection of content.