This is one of the pitfalls of the chat notification system being "smart" rather than dumb.
According to this post on SE: Meta when the system detects the use of a name in the chat box, it attempts to route the notification to the correct user. Unfortunately this sometimes results in another user with a similar name being sent the notification incorrectly.
[The System will] generate a notification for you ... when we
can't find anyone else who we consider to be a better match, i.e.
someone called "Marc" who was in the room during the past seven days,
or someone called "Marc Gravell" who was here in the past two days.
As the saying goes; it's not a bug, it's a feature.