I dont think you can get caucht by stealing bitcoins do you know why because bitcoins are not from you they are from everyone who has bitcoins because they are not on your name.
If you use the stolen bitcoin and people can link the spending with you, then you will be caught. It is better to mix it.
Stealing is illegal no one will tolerate that action, and base on the OP statement i think that is not form of stealing he only a lucky person that generate bitcoin address with a free bitcoin balance in the wallet.
Even for the case of OP, if he gets chances to return those bitcoins, ignoring the and keeping must be considered as stealing bitcoins. We need to act based on our heart not by mind. When we get chances to return the bitcoins we got due to some mistakes, we should return, else it is kind of stealing only.
let us take this to the real world. if i steal someones door keys and use them at their home i am breaking in. but if i find the key and use them to enter the house, this would be still breaking in by the standards of most people. but if i take a piece of metal and make a random key, then go to a random house and the key fits the lock, then this would be not breaking in, but most would say it feels still wrong.
this is the same with a stolen wallet, a found wallet and you a random generated key that has some founds in it.