I could see either scenario that he defaulted to his personal religious belief as the easy 1 sentence explanation that does also include the factors I listed in my previous reply that go far beyond his own personal beliefs but the tangible effects that a Muslim player from a Muslim country has on that players' family and his own well being/opportunities when he visits his country. If he is just passively disinterested, but knows that wearing the armband would be an end to his international career (no idea I'm just speculating), or would lead to issues for him back home or cause his family issues... Why would he wear it? If he's passively disinterested, he'll prioritize the stuff he actually cares about (himself and his family).
In summary, not everyone has to support somebody else's cause and it doesn't make someone a cnut for not joining in on a protest, and this is literally a form of a protest.
As a side note, all the people going hard on the criticism, how many pro LGBTQ protests have you been to this year? How many pro Palestinian rights protests? How many rainbow stickers or laces thongs do you have to show support? Does saying 0 to any of these make you against it?