From the linked blog, he wasn't taking part in organised events, just running the marathon distance on his own, starting at 3am, following a number of different routes in London.
From the linked blog, he
says he was running a marathon almost every day for a month, starting at 3 am each run day.
One method that's been proposed, when there's a concern that an artistic work might have been AI-generated, rather than being an original work of the artist, is to ask for the work by-products.
A finished painting should have sketches and studies, some of them substantial works in their own right, as by-products. Same with a book. If it was written by a human, we should expect there to be multiple drafts, and correspondence between author, editor, and publisher along the way.
One could ask similar questions here. If his blog says he's running a marathon almost every day for a month, what else does it say? Does it have entries recording the original idea, the planning, the prep, the training? Does it have accounts of all the other fun runs and personal challenge runs he's done, since running seems to be such a big hobby for him?
When I was part of an avid bike riding community, it was considered
de rigeur to post a photo of your bike in front of some road sign, landmark, or other point of interest along your latest ride. Does Arday post any selfies of himself, in the predawn light of various London neighborhoods, mid-run?
I'm not saying he has to post these things in his blog. It's perfectly legitimate not to. And if it were just that one claim - gym teacher and fitness freak runs a lot of marathons for personal satisfaction, but doesn't document much of the effort - I'd shrug and move on.
It's only when every single claim he makes in his self-narrative is on that level of accomplishment, that every single claim becomes suspect. The more impressive the claim, the more suspect it becomes. And once one claim turns out to be bogus, every other poorly-documented claim he's made loses all credibility.
There is no world where "I was lying about the other stuff, but the 30 marathons in 30 days was real" isn't a ridiculous excuse.