confirmation time limit
The difficulty of the network adjusts in proportion to the hash rate, so that on average a block is found every 10 minutes. Of course, it's still a random process, so sometimes blocks are much shorter and sometimes they're much further apart.

As a result, if more hash power gets added to the network, the difficulty has to go up to compensate. Otherwise doubling the hashrate would result in one block per 5 minutes instead of per 10 minutes.

I don't understand where you think there is a contradiction, but feel free to clarify.