Chord Progressions

Hello, My Favorite Song of the Day is Loquat's Shaky Like The Flu. It's main progression is G, EbMAJ7, Bb, D7. I have been trying to understand this from the perspective of the Circle of Fourths and Fifths. After the initial G, I'd expect a C or a D, but they go to a EbMAJ7, which I think sounds lovely especially because of how the bassist emphasizes it; however, I don't understand theoretically why these chords work. Are all of these chords in a particular key? Perhaps someone strong in music theory can offer insight. Thanks.