Seems like he took a ferry from Calais to Dover

https://www.runnersworld.com/uk/news/a63224509/deo-kato-lond... https://www.instagram.com/p/DDynCvFAph_/?img_index=1

Looks like you could walk, in theory (but not legally):

> During one Sunday in October 1993, Wally Michalski and Mike Turner, working as contractors on the British side, used a pair of the Saracen bicycles to cycle the 100-kilometre (62 mi) round-trip from Folkestone to Coquelles and back again. The pair took around five hours to complete the journey, while wearing full overalls and needing to carry respirators.[1]

[1] https://en.wikipedia.org/wiki/Cycling_in_the_Channel_Tunnel

Looking through his Strava, I don't think he did?

He reached Calais on the 19th and started from Dover on the 20th, so I'm assuming a ferry.