It's likely that the two different Hanja 金龍鶴 , and 金龍學 is what caused the mix up. Kim Yong-hak official Hanja is the former, as for the latter, you get this sometimes, I've noticed through my research that sometimes unofficial Hanja are used, maybe down to mistranslation or maybe they didn't care enough to get his Hanja when filming etc. Just one of the many pitfalls I've come across when translating Korean film credits written in Hanja, it'd be so much simpler if it was all in Hangul

https://hkmdb.com/db/people/view.mhtml?id=110598&display_set=eng
Cheers