He can click on profile -> Ignore Boards Preferences, to uncheck it.
Uncheck the Altcoins discussion section, let's see what you will get.
It would work perfectly and he will be able to quote the user's post that he wants to quote.
If a board is put on ignore, it will not appear again through the forum home page, but what I think that happened is that BitcoinGirl.Club opened the altcoin board already before in his browser, but later put the altcoin board on ignore. If done like that, he will still be able to access the altcoin board through the altcoin board link already opened in his browser, but forgetting that he put the board on ignore.
I guess some people can leave a link opened on their browser for days, weeks...