If anything, if it was nonman, the last thing they would find would be aporetic runes.
As for the runes themselves, I see no real reason for them, regardless of who built the place.
The Vizer was sorcerous and lived there, could be that he was bored or just studying sorcery for some reason or another. Either way, there were text about sorcery and/or magic, and runes etched into surfaces, so someone had some interest in the subject.