Map 6 Thanos - Bug Or Not?

FPC3

This morning I was fighting Map 6 Thanos. We had had some issues with timing and were down to the last 8 minutes. I got him down to about 40% health remaining and took a Sp2 to the face (slipped up with the reverse controls). Back at the map screen, 5 minutes to go, I saw one of my alliance mates initiate an attack. After a little bit, the fight ended, and suddenly Thanos was at 90% health remaining. There were no nodes still up on him, and I don't recall him having any healing mechanics to his abilities. Long story longer, we weren't able to get him down in time with the unexpected heal. Bug or am I missing something in his abilities?