Just ignore it, it defaults in a few seconds anyways.

Still waiting... no defaulting...

Rebooting and trying again.

This also happened to me with some interesting things. What Linux distro ?
What were the conditions ?

I've come across this a couple of times and an Internet search always came
up with the user name and password to use with the live CD. It is often
something obvious (once you know the secret!) like "user" password "user"
and "root" with password "root". This is only a temporary thing so it
doesn't need any security.

Not sure about current versions, but one or two older versions I tried out
all I did was type whatever I wanted in the user and pw fields. Still
started the system...

Under TinyME it is guest, password guest and root, password root. Nice.
Slax and Puppy Linux log in as root automatically. If you start Slax in text
mode you have to log in. User name: root, password: toor.