We know Squall knows Zell, Seifer and Quistis at the beggining of the game.
They know Selphie“s name because she told them.
They know Rinoa“s name because she told Squall and he told the others.

But no one told their names to Irvine.
And I don“t think he have access to their contract paper.Only Squall had.
Yet he knows their names right on their train.

This is another indication that Irvine remembers them from the orphanage.