Standard "I Am Not A Lawyer" disclaimer, but I think you can safely click on the link saying the claim of infringement is not valid. Here's some history on the tune from the Fiddler's Companion web site (a useful resource for looking this kind of thing up, as well as the tune database on thesession.org):
"MORRISON'S JIG  (Port Uí Mhuirgheasa
This well-known tune is named after the renowned Sligo-born Irish-American fiddler James Morrison, who recorded in the 1930's, however, Morrison did not compose it but rather had it from a Dromlacht, County Kerry, accordion player (a member of his band) named Tom Carmody who knew it as "The Stick across the Hob" (Taylor, 1992). Carmody learned it from his father, Maurice.
That info (if accurate) establishes a tune "written" well out of current copyright protection, and what most folks would consider "traditional" at this point.
Just for grins, I looked up the tune in the Harry Fox database (the outfit that licenses recordings here in the USA), and there are four separate listings for Morrison's Jig, all by different people not named Morrison or Carmody. I believe these are for specific arrangements of the tune, not the tune itself. For example, one HFA listing is for an old recording by the guitarist Davey Graham.
If you're not copying someone else's arrangement of the tune note for note, then I don't see any reason why you shouldn't be in the clear. But again, IANAL. There are hundreds of videos of people playing Morrison's Jig on YouTube, and your upload probably just triggered an automatic note recognition program that thought something in your intro sounded like a different tune that's under aggressive corporate copyright protection (i.e. some recent, major pop hit).