i would think it was a unilateral contract? acceptance does not need to be communicated, it can be constituted by conduct (Carlill suggests this, the advertisement implied that acting upon it would be enough to constitute acceptance. Also Attrill Dresdner v Kleinwort, where you employer tells they have established a bonus fund and says 'if you work well, you will receive a bonus', you don't need to communicate acceptance, you simply work well i.e. perform).
on this view, the nature of your reply after receiving offer (should you bother to send one) is not legal. if it were to have a legal nature, it would be the same as Errington (son) saying to Errington (father), I haven't paid the mortgage instalments on the house yet, but i accept that you have made this offer to me, can i have the house?
generally a unilateral contract need not be made to only one person or made to lots of people, it can be made however (in an advertisement to lots, like in Carlill, or to your son and his wife, like in Errington, or to one person in the case of a conditional uni offer). The university, having made you a CONDITIONAL offer has an obligation to allow in once you've completed performance i.e. achieved the grades.
with Moran, the thing was that it was an UNCONDITIONAL offer, so they (accidentally) sent him an unconditional offer (constituting an OFFER in contract terms). he sent them a letter of acceptance (ACCEPTANCE in contract terms), and consideration was his refusal of other opportunities on the basis of the offer. here there is a bilateral contract created, because the contract was never dependent on performance, Salford University never actually said 'if you do X, we will do Y' (the form a unilateral contract normally takes).
NB: in Salford the court decided the offer was never supposed to be made to him so it would be unjust for the university to have to allow him in, this is more an issue of what happens when an offer is erroneously targeted but accepted in good faith, only the person to whom you intended to make the offer can accept it (i think)