[rando444]

You either logged your new account into a mobile device and it pulled your contacts, or you gave facebook your phone number for account recovery / two-factor and they already had your contacts either from your old account, or if you use whatsapp or instagram.

[huehehue]

I don't use whatsapp or instagram and have not used the new account on any other device.

I did use my real number for the old FB account, but used 555-867-5309 for the new one.

[rando444]

You can't provide a fake phone number for account recovery / two-factor authentication, as they verify that you control the phone number before accepting it.