In an interview with Today FM in New York last November, Byrne said The Gathering was "a sham", describing Taoiseach Enda Kenny's launch of the marketing idea as "offensive".
Miley, a former Fine Gael general secretary, said Byrne was disrespectful to the Taoiseach.
Moreover, the actor recently admitted his use of the word "shakedown" was wrong.
Miley said Byrne was seeing Ireland from the prism of first-generation Irish Americans concerned about using paddywhackery to target the 70 million Irish diaspora worldwide.
The Urban Dictionary defines paddywhackery as "the fakey, out-of-a-box Irishness that insists on the same damned songs and the same damned menu and the same damned Guinness ads on the wall of every Irish bar outside of Ireland".
Sports bodies, local authorities, business interests and individuals are all helping to bring groups of people together in Ireland this year. Already 3,500 events have been organised, some tied in with local festivals. The headline message is 'Get involved'.
The Gathering was developed by Failte Ireland, which targets holidaymakers in the Republic with help from Tourism Ireland, which markets the island overseas.
The Government is providing €5m in funding.
More than €1m is going on advertising and PR, using agencies DDFH&B, PHD and Q4.