I don't think more context is needed, lets not be coy, look up the word inference... Also lets decipher the coded language... "These guys are ...worried about your presence in our store"... They are not talking about a separate group, the manager clearly explained about their presence, that group, in their store...
Then he adds, "we are a bit worried that you MIGHT steal something"... So he has already place on them the intent to steal... from his words or lack of words, there is no indication that he has seen these students steal before, but for some reason... he suspects they MIGHT steal.
Also a third piece of the puzzle is the apology from Apple itself... if the manager was right to kick them out, why would Apple apologise?
They apologised because of the inference, that the group was targeted because of their race, and thought to maybe steal something also because of the factor of their race...
So... yeah... not entirely clear why the manager said what he said and did what he did, but inferences can and should be drawn.