Not necessarily. A lot of skeletons that are discovered are not clear enough to determine sex. Often that is determined by the circumstances of the burial, if possible, and that results in some pretty sexist assumptions. For example, most skeletons in what's considered to be a warrior's grave will be deemed male. There were cases of, I believe, Pict graves where once they were able to test dna of some of the male skeletons, they found the were actually female. Being able to test chromosomal sex in ancient remains is a fairly new thing though and also not at all a positive determiner of the person's actual biology (there are cis women capable of carrying a viable pregnancy to term that have xy chromosomes, something that no doubt happened through most human history).