CIN1 but no HPV?

I was referred for a colposcopy after going to see my GP about post-coital bleeding. I had a cervical biopsy taken after my colposcopy showed 'mild acetowhite changes'. The results of the biopsy have come through (after I had to chase it up when I hadn't heard anything for 2 and a half months!) and I have been told I have CIN1, and have been given a follow up colposcopy and smear (despite being under 25) in a year's time. 


I am concerned because I haven't been told what has caused this CIN1. I phoned up the clinic and the secretary told me that it is generally caused by HPV however this is something 'everyone has and it just flares up and can cause these cell changes', is this true? Or can I have CIN1 without HPV? The secretary said that HPV isn't something I could have caught like an STI or should be concerned about passing on but I am sceptical as I have read otherwise. I received the HPV vaccine about 10 years ago so I'm not sure how it would have caused abnormal cells if I am vaccinated? 


Other than the PCB I have had no other health issues to indicate HPV/cell abnormality.


Can anyone shed any light/reassurance for me?