Looks to be some mistakes in the pricing, judging by the scale of the discounts and the fact that a lot of them appear to changed to more reasonable looking discounts.
I suspect that for a small number of orders at these mistakenly low prices Sigma may have accepted the loss and shipped anyway, but judging by this thread though they might have a LOT of these especially if it’s been pickup by one hotdealsuk or similar sites, and so realistically will probably have to cancel orders that were placed at daft discounts. Lets wait and see.
Their T&C’s allow them to do this, as the state that the contract is formed when a dispatch note is emailed, and they also state that they can cancel an order if “any of the goods were listed at an incorrect price due to a typographical error or an error in the pricing information received by us from our suppliers”