Maybe you were lucky or you must have said something that made them think you opened it for another person.
from the link above on Fido website:
What you should know
Before you start referring your friends, make sure of the following:
You must have been an active customer for a minimum of 15 days and you must use a different referral code per referred friend.
You must get a referral code before your friend activates a Fido number. Your friend must provide the referral code to the representative before the line activation process starts (or during the activation flow if activating service online).
Both of you must keep your services active for a minimal period of 90 days, at which time the credit will be applied to both accounts.
You can only refer individuals with whom you have a personal or family relationship to ensure compliance with Canada's anti-spam legislation. That is, you're either related to one another or it would be reasonable to conclude that you have a personal relationship with the person (and in each case the relationship includes direct, voluntary, two-way communication).
You cannot refer yourself. If you have multiple lines on the same account, the name of the user must be different.
Certain types of accounts are excluded from the program.