-70 Celsius isn't just an unusual temperature it is nearly impossible to maintain without specialized freezers and dry ice, probably one of the reasons we didn't buy more from Pfizer, it doesn't just have to be transported at that temp it has to be stored at that temp, Moderna's can be transported at a normal freezer temp or slightly lower and stored in a normal medical refrigeration unit, basically the temp of a cold house fridge
I didn't say unusual temperature - I said it was an unusual condition (related to storing the vaccine which you explained perfectly) which they had to deal with.
But I don't know why that would be a reason regarding the purchase of additional vaccine, since they are going through the trouble of setting up the procedures (including the freezers) already. Having more of the Pfizer vaccine would better cover the expense of using the freezers, etc.