This seems a correlation not causation argument?
If it fluctuated the same way on a daily basis last week then it's hard to attribute the same 'minor' fluctuations today on TMs announcement
sometimes it is dubious to attribute market moves to news stories, it doesn't seem to be the case in this instance - it had dropped 0.8% over the course of the morning then spiked upwards when the rumours started about Leadsom dropping out before lunch

significant move in the context of a longer time frame? Nope... but that wasn't what was claimed... despite one poster seemingly trying to create a straw man out of that