No! Anyone with the link can join the stream without needing to log into a StreamYard account. They also don't need to download any software.
If you want to require guests to log in, you can turn on the "guests must authenticate" option in Settings > Guests > Check Guests Must Authenticate. This allows you to ban them from your studio, if needed.
This is what your guests will see before entering your broadcast studio.
If you want your guest to be able to add their own channels/pages as destinations for the stream using the Guest Destinations feature however, they will need to have a StreamYard account with us and log into it. More info here.