See, this is my opinion: we all start out knowing magic.
I want someone here who knows magic, and who can catch them if they get away.
Got a phone call this morning off, you know magic?
I need to talk to someone who knows magic.
Knowing magic, though, I would expect the reason to be more complex.
A wizard knows spells, and magic, and can read the thoughts of others.
"But were they afraid of my discovering there was someone who knew magic in the city?"
She does know magic, a little magic, but she's not evil.
"I realized all along that she knew magic," he said quietly.
I think they knew magic like that would frighten my people.