Neither the iPad or the iPhone has ever had Voice Recognition to only allow commands from a single person. It has never worked that way and for personal information to be accessed, it requires the device to be unlocked by you to protect your data.
The only device that has Voice Recognition is the HomePod for accessing personal information. The reason for that is because there is no other authentication method available.
Turn Siri off and turn it back on. This will walk you through the set up process again. The steps provided here are not for Siri to respond to ONLY your voice, but does help to make sure Siri is activated when you speak the activation command. This is more for when Siri is not recognizing your command, but I would still recommend setting it up again.