I may be wrong but my understanding is that this is not correct as there are no means go straight from the gate to the nearby UC for arriving passengers.

You would first have to walk to the immigration and security area to cross channels that allow transit passengers to be in the departure area of terminal 2. I believe the immigration and security are in T2A, or close to it, so to get to the United club from a United gate would be about 10 mins walk to security and about 10 minute walk back and then add another 15 mins to get back to T2A to take your LH flight (this is longer than for arriving pax as there are moving walkways for the latter).