Yes I think it's that.
According to the FAQ, no :
Q: Will the SX OS for people who bought it 'stand alone' be delivered before the SX OS for people who bought SX Pro?
A: Not necessarily. SX Pro will be shipped in the days to come to distributors. SX OS will be unlocked a bit after the reviewers get their units (all reviewers receive SX Pro).
So depending on the speed of delivery to your distributor and then to you, SX Pro could come before SX OS stand alone. It probably will be very close.