While you were out, a person called Mr. Brown came by.
Literal
Absence-during Brown [quotative-と] say person [subject-が] came [emphasis-よ].
ブラウンさんとおっしゃる方 uses the keigo verb おっしゃる (to say/to be called, honorific) and 方 (かた, person, honorific). This is respectful language for describing a visitor — the speaker is being polite about the person who came. こられました uses the honorific passive form of 来る.