Nope, what? You didn't indicate which you were saying "no" to, nor did you indicate what data was synced - contacts, calendar, files...?
- Contacts and certain other data will sync if you have them stored on a cloud account (Google, Outlook/Exchange, Yahoo, iCloud, etc.)
- The dealer can often transfer contacts from one phone to another at the store. Maybe they did this without you noticing
- Your contacts may have been stored on your SIM card, thus will transfer from one device to another if you used the same SIM (you mentioned you changed carriers, so likely this isn't the solution to your question, but may help someone else)
- Your desktop computer, running some app you set up in the past, transferred the data for you if you plugged your new phone in since receiving it
- Files/documents can sync if you use a cloud storage service like DropBox, MS SkyDrive, Google Drive, Box, Amazon, etc.
Other than those 4 or 5 options, I can't think of any other way your data was synced. It didn't transfer by magic, so choose one of the options above.