The relevance within HEMA is not about using historical martial arts to fight police but rather using the training centers to recruit and provide training for such activities as participation in mob shield walls and grappling.
I don't think they are teaching people to use swords to fight police, although Valkyrie in particular (mentioned by the blog) does have training about trying to make swordfighting relevant in military and police situations, so who knows
Again I don't think it is about using actual historical fencing techniques but more that they are tapping into the community of people within HEMA, using the infrastructure of the community such as using the club location and resources meant for historical fencing under their nonprofit and insurance company, for also doing antifa training.
It is something happening in the community per the evidence shown in these posts
https://fightersagainstnarccistic.tumblr.com/post/626484943349022720/far-historical-fencing-blog-that-promotes-antifa
https://fightersagainstnarccistic.tumblr.com/post/624699657862381568/additional-narcissistic-abusers-who-assist