Nowadays, girls are socially discouraged from showing interest in STEM[3], and women who make it past all that to go into STEM fields are still strongly discriminated against[4].
You're right that the article isn't clear about what it means by "computing skill". However, its foundational conclusion - that simple tests show no difference in basic computer literacy but do show significant confidence differences - is unsurprising and reflects what women have anecdotally reported as their experience for years.
[1] https://www.smithsonianmag.com/science-nature/history-human-...
[2] https://en.wikipedia.org/wiki/Glass_escalator
[3] https://www.aauw.org/resources/research/the-stem-gap/
[4] https://www.fastcompany.com/90548817/why-so-many-women-in-te...