The rumor is they actually tracked the song to the drum track from "Let's Get it On", then dropped their own version of the drums on top after the fact.
I like Ed Sheeren (sort of), and I generally agree that there are too many lawsuits in music.
But -- if you listen to the tracks back-to-back, or interleaved, it's pretty obvious. Upon listening, it seems to me the tracks are even more similar than "Blurred Lines" and "Got to Give It Up". Uh oh.