It's more of a grassroots thing, different protests are organised by different people and do not need to be affiliated to the BLM US or BLM UK organisations.
The fact a co-founder of an organisation identifies as Marxist doesn't mean the BLM movement is Marxist. If he had identified as a toy-train collector it wouldn't mean the organisation was about toy trains either. This is something else people have trouble realising. No political movements are created to represent every belief of the founder, they have a more specific purpose that is ultimately determined by the wider body of supporters. Organisation just helps create a common identity, like branding, that local spin-offs (or the Premier league) that share the primary objectives of the moment are free to use.
Here's an article about how the Bristol BLM protest was organised (hint: it wasn't by BLM US or BLM UK):
https://www.vogue.co.uk/arts-and-lif...matter-protest