Firstly, if that happened, it happened with the Boateng guidance back in 1999. I believe I wrote back then that it was fixing the wrong problem and all cycleways should be preferably brought up to the minimum standards seen in neighbouring countries (and finally in England&Wales since 2020) or, as a last resort, the cycleway stopped up and the adjacent carriageway speed limit lowered to 20mph to allow safe mixed traffic. But ministerial instruction to ride on pavements is what we've got.
Secondly, it only excuses those "who show consideration to other pavement users". I suspect the victim in this case was one who would do that, but we never get the chance to see it on the CCTV because of the pre-emptive attack.
Thirdly, this stretch appears to have been a cycleway after all, not merely the pavement.
And most importantly, if you see someone breaking the law, you're still not normally allowed to kill them! The shoot writing in the Spectator seems at pains to ignore that this was not merely someone "who objects to a cyclist in his or her pavement path" and "put my hand out to keep an intruding cyclist at bay" but someone who went on the attack violently, effing and blinding. It also seeks to excuse the author failing to follow the highway code in several ways, including "hooting at a cyclist, taking one hand off the wheel to point demonstratively at the mostly empty cycle lane that has been expensively paid for with my taxes". I bet she's never ridden at that cycle lane and has no clue about the relative amounts spent on motorways, motor-dominated carriageways and so-called "expensively paid for" cycle lanes.