What's even more interesting (and mindbending) is that he is suggesting that if a baby was born 10 minutes BEFORE Joseph died, then they would be of the same generation. By this logic, a child born 10 minutes before Fred Franz died in 1992 would be of the same generation as Franz. In other words, someone 23 years old right now is of the same generation as someone born in 1893.
The WT's use of the Joseph generation scripture is really quite ridiculous. Joseph and his brothers were of the same generation not because their lives overlapped, but because they were all brothers, born of the same man. Moreover, given that a woman's procreative timespan is relatively short (less than 40 years) and given that their four mothers were all contemporaries of each other (Rachel, Leah, Bildad and Zilpah, if I have that right), the brothers would not have been dramatically far apart in age--less than 40 years from the oldest to the youngest--in all likelihood. Again, fitting with the Biblical generation.