Wha?

"Erik was over there at the park last night"
"What Erik?"
"You know Erik!"
"Erik Erik?"
"Yea, Erik Erik."
"Oh"

(name changed of course)

This is a typical conversation that happens in my class at least two or three times a week. I do not understand how they go from not knowing who the student is to knowing exactly who it is with no additional information being given.