[2021] Question regarding invites.

I received an email which says that I can invite up to 5 friends but I have people in my friend's list that I think registered and that I have not send them invites. For example, there is 3 people who registered and in the account it shows 2/5 invites left but haven't sent any invites.

Why is invites counted toward people who registered but not invited by me?

Is this a bug?

Thanks