Someone called me claiming to be an old friend and it sounded like they were using a voice disguiser?

i got a call from a state that i used to live in, and the person that called me claimed they were my ex, kevin. kevin now lives in california and he said he was back in oklahoma and i noticed the voice sounded like someone had been using one of those machines that disguise voices (you know, like those ones on the movies where criminals are talking to the police and disguising their voice?) well i said that his voice sounded weird and his response was that he thought it was the reception. about 15 minutes later, i was curious and decided to call the number back and it said it was disconnected and no longer in service..? what im thinking is that someone called pretending to be him and disguised their voice, and used a fake number so their's wouldnt pop up on my caller id. kevin and i havent talked in a very long time, and we have no reason to because i am now married and pregnant and have no contact with him at all. and im 100% positive that he woulnt have my home phone number, and i also dont live in oklahoma anymore, and im sure he has no idea where i live now. how could someone disguise their voice and use a bogus number to pop up on my caller id? what do you think is going on?