First of all, institutional sexism is posting about gender diversity only on 8th of March because it’s acutely aware of the marketing potential. I went through the poster’s and the company’s history and the website and there were no other mentions of it before or since.
Institutional sexism thinks that the benefits of diverse teams have only recently been discovered. It also thinks that any sort of benefits derived from inclusiveness and diversity are shocking to everyone else as much as they are to it.
Institutional sexism recognizes that times are changing but it’s just something that must be done, even if you hate it. Like eating your veg.
Broadly, it’s either resisting the change (“complaining about it”) or is at best passive about it and only doing the bare minimum to qualify. Such as putting chairs in toilets and calling them nursing rooms.
The author also seems to disregard that it’s unlawful to discriminate based on pregnancy. But legality is not really a problem for institutional sexism.