[Benjamin]

This is an excellent question! It is true that the following translations generally hold true:

mannum ‘who?’

mīnum ‘what?’

As we introduce mīnum in a later lesson, this is how we use it (see lesson 6.1 and the phrase mīnum annûm). I think it might also be in an earlier lesson as well.

However, because the word šumu(m) ‘name’ is so close semantically to the person who bears the name, sometimes the conceptualization of šumu(m) can be more like a person than a ‘thing’: i.e., something of a blending between ‘who are you?’ and ‘what is your name?’.

This is the explanation, but of course it all comes down to the evidence. In the Epic of Gilgameš, we find the following text:

sursunabu ana šâšum izzaqqaram ana gilgameš:

mannum šumka qibiʾam yâšim

…

gilgameš ana šâšum izzaqqaram ana sursunabu

gilgameš šumī anāku

‘Sursunabu spoke to him, to Gilgameš:

“What is your name? Tell me!”

…

Gilgameš spoke to him, to Sursunabu:

“Gilgameš is my name.”’

Here, the phrase mannum šumka is used for ‘what is your name?’. Note that the various Semitic languages exhibit variation on this point. While Biblical Hebrew normally has מַה־שִּׁמְךָ ‘what is your (ms) name?’, it once has מִי שְׁמֶךָ ‘who is your name?’. Aramaic generally has מַן שְׁמָךְ ‘who is your name?’.

Hope this helps!