Didn't watch the video very closely but I've seen similar tricks in which you cleverly disguise the fact that you're dividing by 0 at some point in the problem and thereby get ridiculous answers such as 0=1 and 4=5.
Oh yes, the Irish may not be good enough to win but we can at least spoil the English "grand slam" party. In a perverse way that's even better than winning the trophy.