Fingerprint is not just used for locking or unlocking your Moto G5 Plus phone, it can also be used to unlock the apps on your phone. You will have to install a third party app to do this. You might have used the App Locker apps earlier, where it will ask for some passwords or to draw the pattern to unlock the apps. The same apps are now upgraded to recognise your fingerprint.
There are lot of App Locker apps available on the Play Store, among them are the App Locker, CM Security Master App Lock (Which comes with both AppLock and AntiVirus). You can go for any of these apps, once installed it will ask for the list of apps that needs a lock. Select the list of apps to be locked and you are done.
Next time when you open any of the apps that were locked just use your fingerprint to unlock it, there is also an option of drawing the pattern. Make sure when you install these applocker apps from the Play Store it supports fingerprint sensor else you might just have to use the patterns. I would recommend to go for the CM Security Master App Lock which comes with both AppLock and AntiVirus.