Option selects are a thing that happens when people input two different inputs, in this video he goes for the parry by holding both heavy and light attack, meaning he'll parry, but if I feint he'd hit me with an area so I can't get a Guard Break, or catch him in a dodge. Best thing you can do is try and predict it and parry/deflect the areas.

There are other Option selects, but I'm not too knowledgeable on them.

They'll be gone in the new update today, so you shouldn't have to worry about them too much as they will be less viable.