We would need a little more information. There are literally about a dozen different ways to have a motion sensor notify you on a smartthings system. So what did you set up to do the notification? Was it smart home monitor? Notify me when? A routine? Something else?
If it was smart home monitor, you may have been confused about the fact that the “away” alarm status is not the same thing as the “away” mode.
If you weren’t aware that the word “away” is used in two completely different ways in smartthings, the following thread might help. (This is a clickable link)