Only he knows the reason why he wanted his account to be disassociated from the thread but my guess is because he doesn't want to be related or involved in the donation thing especially he is the one who posted it and if situations (charity or something like that) like that turns out to be a scam even though your forum account is only an instrument to use to start or create the thread but still you will be blame for it and get red tagged then you lose people's trust. It's just my OPINION why it is anonymous even though you would know who started the thread as theymos said.
You can change the OP's author name, but the OP's situations don't change with that.
The fourth answer in the topic in question has a quote from the author:
When clicking on the link in the reply would also redirect to the original post which I just tried right now.