How is it possible that they can hide the transaction or not show it on a chain? Or does this post mean that a specific pool did not pick it but was processed via another pool?
They simply choose not to include the transaction in any of their blocks, so it remains unconfirmed until another non-censoring pool (hopefully) includes it in one of their blocks.
What is the technology that they are implying here that is calling them to do so?
The US government publish a list of addresses they want to censor. The mining pool refuses to include any transaction with pays bitcoin to or from any of these address.