Mobile phones and Facebook

Hi, recently I gave my mobile number out to someone I was chatting to and they responded knowing my name. One way I thought this may have been possible was if they typed my mobile number into Facebook in the search field my mobile number is not in my profile however my phone was synced to messenger and my mobile number was in my contacts list. Does this mean they would still be able to see who I was? Or do by freak of nature they know me and somehow had my number already installed on their phone.. As I said the number wasn't in my Facebook profile under contact info but I did sync all My phone contacts in messenger.