NTA. It would be a cold day in hell before I apologized to a landlord like yours. You dealt with the invasion of your privacy perfectly. As a renter, I would be thrilled if the departing tenant informed me of a landlord's mistreatment his tenants. I would have dodged a bullet thanks to you.

As for getting your deposit back, your landlord is silly claiming he has a legal right to keep your deposit just because you dissed him to potential renters. Do go online and check on renters' rights (aka tenant's rights) in your state and/or city. For example, here's a publication from my state's Attorney General that is very explicit (see page 24) about the law regarding the returning of security deposits for apartments. I'd also take take some video of what every room in your apartment looked like right before you turn in the keys. Good luck and enjoy you new apartment!