Kurt runs up the stairs and is startled by marching band members coming around the corner at the top. He turns and starts down the stairs, miming being a drum major, with musicians right behind him. When the angle changes, the musicians aren't in the shot yet.
In recalling how Tina's relationships ended, Blaine states that Artie broke up with Tina after learning that she had been faking her stutter. Artie was angry, but either he didn't break up with her or they got back together because Tina dumped him for Mike between the first and second seasons.
Santana couldn't have recognized Paolo and Rupert at the Spotlight Diner or known who they were in relation to Rachel; she hadn't met them yet.