Questions for owners who let cats outside

I happened to see the motion-activated lights outside my front door go on a few minutes ago-around 1230am. There was a cat eating from a trash bag that had yet to be brought around to the can. I see cats roaming my neighborhood a lot at night.

So, my questions for those of you who let your cats outdoors, are:

1. do they generally go out at night?
2. would a well fed cat rip into a trash bag for food? I know my cats have torn iinto their dry food on more than one occasion.

What I am ultimately trying to ascertain, is whether this cat is a stray. I know I have posted questions about this before but maybe most of the cat owners n my neighborhood have outdooor cats. Having rotten, uapproachable neighbors doesn't help because, obviously, it would be easier to ask.

I do know of someone else in the same town, who has been feeding several cats for some time. I don't know what kind of coinfirmation, if any, she has gotten, that they are, in fact, strays. I can't take in anymore cats right now but if it is a stray, I'd like to do whatever I can to help it.

If there's something really tasty in your garbage, yeah, a pet cat might rip into it to get to the tasty stuff. Meat, cheese, etc. If it's something that cats normally wouldn't like, such as oatmeal then the cat is probably pretty desperate for food.

It really can be hard to tell who's a stray and who's a pet :/.

would a well fed cat rip into a trash bag for food? - Yes! They're nosey as much as anything. 

It can be hard to tell strays from owned cats, but strays (rather than ferals who are more adept at living wild) tend to be dirtier, scruffier and a bit beat up. Many have patches of fur missing from flea infestations. If it runs away from you or is visibly scared it is more likely to be a stray or a feral. This obviously varies - if a stray/feral has a good food source and a place to sleep or is newly lost/abandoned it may look very similar to a regular pet. 

You can download paper collars from the internet which have a space for your name and number. The idea is, if they have an owner they'll ring or text you and say 'yeah, this cat has a home'.

You can also check online pet directories and post a photo of the cat to see if s/he is lost or if someone is looking for them.