My GF recently went on a trip she accidentally called but she said it was phone interference, HELP.?

Well my gf recently went on a trip with her friends and she said she was gonna call me every night. Well she called and I answered however, she did not know she called and in the back I heard moaning and it sounded like someone was having sex. They were screaming obscenities and things of that nature. I hung up and called right back however my call was ignored. About ten minutes after she called me and I told her what I heard and she just told me that it was probably phone interference and that her phone was in her pocket the whole time. What could have happened? I want to believe her but I'm not sure if it was a coincidence or not. Please help me.