Imported random wallet that has ether in it

I was just looking through my wallets because I wanted to clean them up. For unimportant reasons I had like 4 wallets and only needed one. Now I'm just checking to make sure non of the wallets I want to get rid of have ether or testnet ether bc that's also tedious to get now. At that moment I saw that I Account 4 had ether in it. Only 0.0005, but still I can't remember this transaction. Than I looked at it on etherscan and see that at one point the wallet had 13 ether in it. I know for a fact that this is not my wallet. Also it has transactions dating back to times where I didn't know about crypto.
I only imported the wallet to see if you can just import a random wallet using a random private key when I didn't know a lot about crypto. When I did that and imported the wallet I did the math and came to the conclusion that there are waaaay to many possible wallets to find one that holds ether.
Also I just checked the private address and I can confirm that I made the private key. How is this possible? The chance of this happening is so small that something else must be going on right?
I only just found out the wallet holds ether. What are the laws behind this? If it is possible to find random wallets can you just steal their ether? Obviously I'm not going to steal this ether, but it would be very concerning if that is possible.

The address is: 0x2e988A386a799F506693793c6A5AF6B54dfAaBfB
I don't think I can share the private key but it is something very obvious like 123123123123123123....