The seed and the PIN are generated in their site mytrezor.com
what makes me wonder if they have access to this sensetive info?
PIN is set by user and it is known by the Trezor device only. Your PC doesn't know it, because of the unique way you enter the PIN, see
http://doc.satoshilabs.com/trezor-user/enteringyourpin.htmlThe same is true for the seed, when a new seed is being created entropy from PC and Trezor device is (provably) mixed in the device to get a new seed. Seed never leaves the device and is only displayed once on the Trezor screen during the initialization to let the user create a paper backup (24 words using BIP0044), that can be used in many 3rd wallets, see
http://doc.satoshilabs.com/trezor-apps/index.html