Your author goes on at length, about the origin of Protestant beliefs regarding the rapture being less than 200 years old. Odd, then, that denunciation would have occurred in 431, and again in 1516.
It would appear that the learned Mr. Guinan has destroyed his own argument, here.
What Mr. Guinan is referring to is the idea of ‘premillenialism’, which was about long before the ideas of the Rapture were formulated in the 1800s.
Rapture has its roots in premillenialism, a doctrine that has long been rejected by the Church.
Though to be fair, he could have made a better distinction between the Rapture and ‘historic premillenialism’.