I voted for "No", I don't think biological sex is a social construct however the notion that biological sex is binary is a social construct.
What do we mean when we talk about biological sex? Do we talk about chromosomes?
Our Chromosomes are non binary, many people have XX or XY but there are also people who have X or XXY, and among those people who have XX or XY are people who have unnormal mutations in that chromosome pair.
Do we talk about genitals?
Some people have non functional genitals, some have underdeveloped genitals, some have no genitals and some have both genitals. In the Dominican Republic exist a weird gene defect where boys are born without a penis and only develop on when thay enter puberty.
So the article is at least right in the sense that biological sex is not so easy as we think.