I am not sure it is worth getting surprised.
Traditionally IWD was about women's workers rights and more often than not were part of a trade union event ie the expectation that men would be supporting women's equality at work. (Better that the Soviet Union celebration of IWD which was for men to give women a red rose and still expect her to do a full day's work and then go home and do all the housework and childcare.)
It was only during the era of Women's Liberation that women only events and marches started to happen (and the TU tradition continued).
But as Women's Liberationists faded away and third wave feminism who went out of their way not to be seen to be aligned with old dinasours, women themselve stopped celebrating IWD.
So a local council having men at one of their events is surprising.
What we really need to be talking about is why so few women are motivated or feel able to organise a women, even a feminist, IWD event.