Who else was on their team? Doompriest? Tuhanarak?

Could be the Resurgent mastery too.

Another option is they were potentially wearing a Deflection set, which allows those debuffs to be transferred to your team occasionally.

It was a tag team with 3 singles.

It could've been, especially against Apothecary. I'm not sure about Rhazin, I wasn't watching the damage inflicted closely enough during that match. 

I didn't realize deflection did that, I haven't looked at it that closely. That's a nice tidbit to hear, thank you!