Lambert, 29, thanked her fellow nominees when she stepped onstage to accept her award.
"Kacey, congratulations on new artist. That was awesome," Lambert said as the camera panned to a stone-faced Musgraves sitting in the audience.
Lambert and Musgraves have worked together before, co-writing Lambert's 2013 track, "Mama's Broken Heart," so it's probably a coincidence. Musgraves cheerfully accepted her own New Artist of the Year Award saying, "I feel very thankful. Thank you so much."
Watch the incident at the 3-minute mark below: