Sending "Clickable" links to unsaved/new number on Whatsapp

Hello,

I am trying to figure out the workaround on how to send this message.

 a spam message was sent by some random number to me. It had a link/button which i was able click, I am surprised how the person is able to send the message with link and yet whatsapp allows me to click on that button "Join Group".

Any of you are aware how to do this? 

I know that only way a link is visible or clickable is "if I reply to original message of that number" or "if I save that mobile number in my contact list"

But, my question is if i dont do either of it, how can i still send a message with an URL which is clickable.