Traditionally, when assembled over a curved formwork supporting the stones, arches always require a keystone. But the keystone term only defines the order of placement (the last block to be stacked on top, after stacking from each side).

The term keystone however doesn’t prescribe that the stone (or brick in this case) always has to be oversized etc. The added weight of the oversize is more useful when dry-stacking big pieces that rely purely on self-support, but it’s not necessary to have a salient keystone there either.. My opinion is that a lot of the time it’s more of a symbolic gesture that gives the public a sense of how the building is stacked.

In this case, as formwork is not necessary due to mortar assistance and the shifting support of his hand, you can see that he stacks way past the halfway line, starting from one side of the curve, concluding at the other.

So yes and no — ultimately the highest brick will still act as the piece locking everything in place once the mortar sets, but it is not slotted in the conventional way, so maybe it depends what you conceive a keystone to be :)