Is the 5.5 BGG rating a placeholder or is that what it really is? Seems super low 0_0
It has an average rating of 8.1 across only 49 raters. That gives it a much smaller Geek rating, which adjusts average rating based on number of raters. Expect the average rating to go down and the geek rating to go up after the game officially releases.
The rating shouldn't mean much of anything until the game actually releases and more people can play it. Ratings at most should be used as a quick glance guideline even in the best scenarios.