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Welcome to the forum.
It is most unlikely that you have been hacked. Hubs seem reluctant to remove devices from the list when they are no longer in use. Seeing as you have a new password your friend can't reconnect now. Just one of the 'strange' features of Hubs.
If you have reset the hub and set a new password your friend won't be able to connect now.
The best advice is not to give out your wireless password. Even if you know the person that you are giving the password to, you do not know how "clean" the device that they are connecting with is. It could have malware or a virus on it and by connecting to your network they could infect your devices.
If you want to let people connect to your wifi I would suggest that you buy a router that supports a "guest" network. This is entirely separate from your own private network and nothing can pass from one to the other. You can also reset the guest password as often as you want without affecting your own private networks password.