wrote:

P.P.S. to our friend in Canada:

Could they get him for drunk horseriding?

I do believe they could.

There have been numerous humerous types of stories on both sides of the
border where people riding things like riding lawnmowers have been
charged with D.U.I. type offences.

In this case because it is not a motorized vehicle they would probably
have charged him with public intoxication.