If you can see someone's location on your phone is it possible that it isn't showing right?

I've recently come across something with a friend of mines iPhone location. He had passed out n checked on him on my phone and it did show he was were he was however about 30 min later I checked n he was like 5-10 miles on some road. So needless to say I was mad cause we had plans. He told me sorry dude I slept longer than I was gonna. Is it possible that the iPhone location is wrong or its it always the true location?

It could be wrong. My phone thinks I'm in St Louis every so often.

Your friend may have other more serious alcohol/drug abuse problems.