The Wikipedia article (https://en.wikipedia.org/wiki/Hydrodynamic_escape) on hydrodynamic escape talks about escaping heavy molecules as if that's the principle function of the mechanism. But in much of the scientific literature on early Venus, hydrodynamic escape seems to refer primarily to the escape of free hydrogen.[1] I'm not a scientist so I don't know what to make of that, but in any event thermal mechanisms (i.e. Jeans and hydrodynamic) can absolutely cause gaseous particles to reach escape velocity.

[1] Photodissociation splits H2O, hydrogen is kicked out into space via thermal mechanisms, and much of the remaining oxygen, too heavy to escape at a significant rate under the local parameters, is sequestered by the molten core, volcanism, and surface weathering. At least, that's how I understand the literature as a layman. The modern debates and research seem to be centered around the particularities, especially the early geology, such as how long core material was exposed.