Can you figure out if your friend is sharing their location from their iPhone or MacBook?
No. Apple lets people choose which device feeds the location for them. Apple lets them choose to share that location with you but not the name or type of system that feeds the geo location.

You get to see that location and not which device they chose to feed the location data. I'm not aware of any Mac client to input from iCloud find my friends, so you can be pretty sure they're not sharing from their Mac due to system design and not due to Apple letting you know what your friend chose. They could use a watch, iPad, iPod or iPhone currently in iCloud Find My Friends app.