I am of opinion that it was a fill done by a computer program of a broker. These are often programmed to trade in one lot increments but at lightning speed if there is sufficient offers available on the other side of trade. In such a case only one lot would be visible at a time and replaced in milliseconds after being filled.

And agree this method is used as an iceberg to impede sp movement in a particular direction.

Just anothr comment from a cheap seat near the rafters of this forum, Cheers, Ed.