non-knights Hero units… Just happend to me and I find it quite weird. I mean, if is that how it is, then give me Knight status as I played also as a Necromancer. 
Perhabs an error?
Are you sure Skeleton didn’t make two simultaneous match-3’s?
Nope… It was a single 4 skulls match. It did like 51 damage, or something alike.
You saw the “-51” graphic? Or you subtracted resulting health from prior health to calculate damage done on the turn?
I saw the number, am 99% sure it was 51.
Was there a massive skull cascade before that?
I had something happened to me where I got hit by a massive load of bone dragon skull cascade; it killed my first guy, and somehow hit my 2nd guy too (which shouldn’t have happened since that skull nerf a while back).
Anyway, the problem is that the damage done to my 2nd guy was not displayed, so it looks to me as if my second guy was still at full health, when in fact it was only hanging by a thread. And the next guy that grazes it basically one shot it immediately. Could this be what happened to you?
It was a single 4 skulls match! 