I know you found out where it came from, but if happens to anyone else, report it to your bank straight away.
It is against the law to keep it knowing it was accidentally transferred to you, and you will be criminally charged, or have to go through the bs of sorting it out down the police station with the person involved. You know, lots of waing, saying " I am sorry" and paying off the cops not to come down hard on you. And with all the hoo-ha about online scamming at the moment, you do not want to be the farrang who got a load of money wrongly transferred to their account.
Usually what will happen is the person who transferred the money, if finding out it was mistake will contact their bank and they will make a request to your bank to contact you to tell you of said mistake. After that, if you don't respond the cops will get involved.