Thanks for that. I rechecked the website and here is what is says.

Undoubtedly the PREMIER power building and muscular development exercise program to come from any area of the Chinese Fighting Arts!! Many physical strength building sets from Kung-Fu claim to be the best at developing the kind of awesome body power that many of the legendary Masters were said to have achieved. This is true of strictly ''internal'' systems, such as Chi Kung (which, if true, takes a lifetime), as well as combined ''internal/ external'' programs such as 5-Family's Iron Vest, Hung Style's Iron Thread, 5-Animal's Muscle Change, or Buddha Style's Teet Lo Han Chin Ch'uan.
It doesn't necessarily say it comes from a certain style, but it doesn't say it was created by them either.