someone calling my contacts but it's not my phone

ok so I was at dinner with my family and my phone started ringing, it was my friend. I didn't answer at first because I was eating. But then she called again so I thought it was important so I answered. It was a guy, and he said he found this phone in a restaurant & wanted to return it, so he called the most recent contact. I was a little bit skeptical because she has a password so I don't know how he got in, but still. Then I said I would text her dad and he could go get it. Then he started rambling about how "he should get at least $50 for this, he could sell it on eBay for twice that!!" & he was also yelling something to a guy who seemed to be in another room. then I just said ok and hung up.

so after I texted my friend's dad, he said that she didn't lose her phone she had it with her right now in the hotel room (we are both at a soccer tournament). I thought this was weird so I called her, and she answered, not the freaky guy. She said she had been in the hotel room for the last hour or so, and her phone had been with her the entire time. She checked her call history and never said she called me at all. So now we were both kind of freaked out.

Then, my our guy friend said he got a call from my girl friend too. he didn't answer. but my girl friend again checked her call history and it never said she called him. I know this isn't really a big deal but we are just 14 year old kids and we're kinda freaked and we wanna know what's up.