What's happening in "Nobody Knows The Trouble I've Seen"?

Hi everyone, glad to be a part of this group. Recently I was singing and playing several songs in D A C but one song I wanted to play was the Spiritual, "Nobody Knows The Trouble I've Seen" which is in Ionian. I chose to use the middle A and bass strings D as a shortened Ionian possibility. I was surprised, however, to discover that when I hit accidentally hit all strings especially to accompany the 5th and 7th fret notes on the middle string that it sounded rather jazzy. Could someone put into words what's happening here?