[snvzz]

>discarded, unused bike rotting in a ditch

Every bike in japan has individual registration or, same thing, a registered owner, as you found out.

You stole a bike, when you could have ignored it or reported it as a lost object.

There were consequences, which shows the system is working properly.

The police were surprisingly kind despite your actual crime, as you did not get the same treatment as the OP.