That's right. Bitcoin-central is a bitcoin exchange marketplace where funds (euros) are deposited to a regulated payment account while bitcoin.de is what is usually referred to as an OTC marketplace.
The main difference is that whenever a trade is executed on bitcoin-central, the fiat currency balance of the seller is credited immediately with the proceeds and the bitcoins are delivered to the buyer.
Conversely, with an OTC mecanism, both the buyer and the seller must wait for the buyer's fiat currency amount to reach the seller's bank account. Meanwhile the bitcoins of the OTC seller are tied up.