Thanks! Will try it for curiosity's sake.
Never enter your actual seed anywhere, unless you absolutely must to recover your otherwise inaccessible wallet. As soon as you type your seed in to a computer, it should be considered compromised and you should transfer all coins contained within that seed to a new wallet immediately.
Is it therefore a possibility that one can steal from it?
Theoretically it is possible (in the same way that all the atoms in a marble statue suddenly vibrating in the correct direction to make the statue move is theoretically possible), but in practice the chance of it happening is so close to zero that it is deemed impossible. See my quote below:
Let's say we have a trillion planet Earths. On each Earth, there are a trillion people. Each person has a trillion computers. Each computer generates a trillion keys a second. All these computers have been creating a trillion keys per second since the birth of the universe 13.7 billion years ago. 10^12 * 10^12 * 10^12 * 10^12 * 60 * 60 * 24 * 365 * 13.7 * 10^9 = 4.3*10^65. This means thay they would have so far generated approximately 0.0000000004% of all private keys.
I think it might be worth clearing up a misconception which you seem to be holding. "Not your keys, not your bitcoin" refers to all wallets. If means if you are trusting someone else to control your private keys (as is the case in exchange wallets and web wallets), then the bitcoin isn't really yours. Indeed, even if you know your private keys and someone else does too, the bitcoin still isn't really yours, since the other person still has full control over it. The private keys need to be yours and yours alone.
Now, you don't actually need to "know" your private keys in the sense of having them written out in plain text and saved somewhere. You simply need to be the only person who can access them. Just in the same way, you don't actually need to "know" your seed in the sense of having it memorized, as long as you are the only person who knows how to retrieve it from your back ups.
When you first use a hardware wallet like your Ledger, it first generates a seed. It then uses that seed to generate all your private keys. The private keys are held within the device. As long as you are the only one who can access your device and your seed, then the private keys are yours. You don't need to "know" them, you don't need to have them saved in a file anywhere, you don't even need to be able to extract them from your hardware wallet (although you can if you wanted).
So to answer your initial question: If your hardware wallet generated a new wallet for you, you backed up the seed, and you are the only person with access to it, then the private keys (and therefore the bitcoin) are yours and yours alone.