But in this case they do matter. When you give someone your phone number, you give them the possibility to contact you. And then it should be securely, if it's possible.
A check for "aliveness" of a number can be done without Signal. Just call and see if it is ringing. You get the same information. Your Signal profile name and picture, however, will only be shared when you accept it.
I understand your frustration, but Signal didn't notify your contacts because you installed it. It notified the other person, because he had your phone number.
Your local Signal installation regularly checks if any of your contacts (with the phone numbers you have of them) are registered at the Signal servers - and then lets you know it, such that you can text this contact securely.
A check for "aliveness" of a number can be done without Signal. Just call and see if it is ringing. You get the same information. Your Signal profile name and picture, however, will only be shared when you accept it.