Nicky Henderson is my favourite trainer, if I have one, but he isn't always clear in his communication to the betting public.
I assume someone inside the yard is letting the side down.
Possibly not DO, if he rang the BHA to let them know of the situation last Tuesday at 0845 then they also knew so could quite easily have starting having fun on the exchanges.
Some interesting observations on Nicky's runners at Cheltenham
https://www.narrowingthefield.co.uk/what-we-learned-from-the-weekend-24th-25th-26th-january/