Who's the boss?

I had a piano lesson tonight with my new teacher, Alexander. This was only my third with him so we're just getting to know one another. Last time, we did some exercises that were very basic but also very hard; sequences that had to be done very slowly but with lots of control, and with a lot of physicality - something I'm not used to on the piano. I can really engage with a guitar, but I'd always thought of a piano as something much more passive - it just sits there with 88 keys and all you have to do is hit the right ones in the right order and you're Oscar Peterson. Or whomever. But Alexander was telling me that it's not enough, I can't just stand back from the piano and just idly play, I have to get more involved. Relaxed wrists and arms, but leaning forward to use bodyweight on the piano, and hitting the keys as though I really mean it. Or, to paraphrase, showing the piano who's boss.