It still is. Just because it includes physical signifiers that can be measured doesn't mean it isn't still a social construct.

To give a contrived example; if I say people with ring fingers over 3 inches long are Longfings and people wkth ring fingers 3 inches or less are Shortfings, and then out society treats people differently based on being Longfing or Shortfing, this is a social construct that is causing problems for people based on a contrived criteria that has no real meaning. The same is true of race.