This is clearly a matter of opinion, deriving (I suspect) largely from playstyle preferences. I would call it combat, even if all the bad guys had been cut down without a chance to act, simply because everyone was on initiative and attacks were rolled.
While this is all very valid, remember that, for some playstyles, this encounter would be great fun. (In fact, it sounded like it was, on the 'cast.) Not only that, nobody knew that things were going to pan out the way they did until dice hit the table and the pcs hacked down most of the orcs before they could act.
Again, this is all about playstyle preference. In many campaigns, some or most evil humanoid types are fundamentally cowards at heart, possibly including orcs. In others, different orcs from different orcish cultures may have different levels of cowardice. So, while it's fine that orcs in your campaign wouldn't be freaked out by humans under the circumstances in the encounter we're discussing, it's not fair to assume that no orcs in anyone else's campaigns would be. And in fact, Mearls' dming proves my point.
Forgive me if I'm misinterpreting, but it seems that you're saying Mearls was doing it wrong. Yet it seems as though everyone at the table had great fun- which is pretty much the definition of "doing it right" when you're dming.
I think a very simple pursuit and evasion rule set would be valuable.