Hello there,
Well it is quite simple ; Montenegro is still very safe!
Probably part of the reason is because it is such a small country, it is hard for anyone to commit a crime, as "everyone is watching you" and it is easy to find you... But it is also not in the mentality here to steal things. I know many people, including myself, who forgot valuables in cafés, or even on a public bench, and a few hours later found them waiting for them.
You also frequently see people with expensive cars stopping next to the newspaper shop, leaving the car engine on, windows down, walking in the shop for a small chat, and coming back out, and.... Oh surprise! The car is still there!!! Everytime I see this, I think to myself that in France the car would have been gone in less than 1/2 a minute....
As for walking alone late at night, also this is something that doesn't feel scary here. Unlike in many western countries, here, girls are left alone, you can walk in the street with a skirt without getting constant comments from guys, which is something you can't really do anymore in France for ex.
So, yes, to sum up, it is indeed very safe. There are like everywhere some crimes now and then, but very little compared to France for example, where I grew up.