I'm not sure how sincere the question is, and I would only expect non-Brits rather than non-Northerners not to understand, but here would be my take:

The irony arises from two contrasting but equally stereotypical views of the fine English county of Yorkshire, namely:

a. To those from Yorkshire it is God's Own Country - as close to perfection as any mere piece of geography could be, and populated with the finest people who live in the most perfect society imaginable; but

b. To those from other parts of England it is a post-industrial grot hole whose towns are full of grime-stained derelict mills and vile concrete council estates, and whose insular people eat unappetising traditional English food and are clueless about all the wonders that the rest of the country/world has to offer.

Neither version is accurate but the contrast provides scope for humour, such as that provided by Hale and Pace, two giants of comedy who are responsible for the video that has been posted.