What’s the deal with workers getting mad if an item is priced wrong.

Found 2 dresses that had a $11 clearance sticker on them, go to check out at self serve and it was showing as $30.00 each. They honoured the $11 price after going to check where I got them from but the worker was so incredibly rude about it and whilst changing the costs told me it’s not even meant to be on sale.