Sorry if I've misunderstood but wouldn't the right to be forgotten also affect the person who filed it? Also, depending on the area of research of your friend, perhaps interst in his research has temporarily waned?
Even if interest has waned, it's unclear to me why that would result in his website vanishing and not, for example, his profile on his employer's website (which is still one of the top results). It certainly doesn't explain why this would coincide with warnings about data protection in Europe. It seems like there's no way of finding out if those warnings are actually related, never mind contesting a takedown.