@uwu
Uhhh... are we even reading the same thing? they literally explained why... the examiner said that Arthur himself was clearly holding back as if trying to hide what he's truly capable of like as if he is wanting to be intentionally graded lower like B rank to avoid attracting a lot of attention, especially the unwanted ones so he looked at Arthur and did some confirmation from Arthur and Arthur gave him a nod of agreement to rank him B even though he can be ranked higher.
Edit: Hope this answers your question