Should users get a notification by the notification bell if a fellow site user puts an @ and their username to direct them to something? For example, I've just @ this chap as per the pic below, and he didn't get one....  If he should, could someone tell me why he wouldn't be?

They should click 'Notification Settings' and see what is set for the relevant item - if "No Notification List" then no notification...

As Nathan mentioned, they would only receive this if they have configured it as such. If there are any further questions, please let us know.