The article doesn’t really expand upon what having fragments copied from others means. Even if it fits the letter of the definition, on a phd thesis that may or may not be a big deal. If he’s passing off the ideas of others as his, or faking his research by using the results of others or making them up, then that’s really bad. If he’s just using phrases / wording from others to get his original points across, it looks bad but I don’t see it as a huge deal, especially 30 years out from the phd.
A PhD is supposed to be original research, if the originality or integrity is in question that’s one thing, the rest is much more pedantic, even if technically wrong.