Perhaps the interviewer is wondering if they can stand to sit next to you for several hours as well as checking your general knowledge?
The sim is important. If you can't fly then it's going to cost you a small fortune in extra sim sessions on top of what you are already paying for the TR. If you fail the TR, and people do fail it, then not only have you got nothing for your money, your sim buddy no longer has a sim buddy and that screws him/her up and it also screws the company up because they've already got big plans for you.
As others say, be very prepared. The 738 is a rocket ship compared with what most are used to, but if you really know what to expect you can get nicely ahead of the game. Remember how tough a light twin was compared to a single? Jets are simple. Push levers forward and scenery speeds up, pull them back and scenerey (eventually) slows down. Thrust/Pitch couple is very powerful. There's bugger all trim change with flaps. Use the electric trim. When rotating count to 4 while doing it. You know when you're airborne because you hear a clear CLICK once the wheels are off the ground. You can then pull reasonable firmly to get through the dead patch and you're away.
In the sim you're a team. Just like the real world.