Are they wrong? Why does a modern person living in Egypt have any more claim to something like Imhotep’s toothbrush any more than anyone else? Just by possession of the land where it was left? I don’t believe in real estate staking an ownership claim. I have more in common with my worst enemy than I do with my ancestor in 4000 BC.
Yes, they are clearly wrong? Modern Egyptians obviously share more links (ancestry, bloodline, culture, geography, etc.) with ancient Egyptians than you do. Whether they have more in common with modern Brits or their ancestors has nothing to do with anything.
Sure they have more links. But why does that give them ownership of Imhotep's toothbrush? If possession equals ownership for land (i.e. nobody is really claiming that the land that Egyptians live on should be given to someone other than Egyptians), why not for artifacts?