Even 50,000 years ago there would be less than 1% DNA trace. This author is just ignorant. My Great Great Grandmother only gives me 12.5% of her genes so my 4th great grandparents would give me about 3%. That is a long way form 50-80 thousand years ago.
You're assuming that the person got 'one shot' of Neanderthal genes 50,000 years ago and that was it. They may have been getting a mixed % of Neanderthal genes from each generation...not just once.