I never quite understood that, it wasn't like they were nobodies. Maybe Moon the loon was chemically altered at the time
It might be because :
1. At the time, they didn't have a vocalist and
2. Page wasn't as well known as anything other than a session guitarist. At least, not until the Yardbirds.
3. This was after the Yardbirds had split up, and Page and others were trying to form "The NEW Yardbirds".
I guess it would be like hearing about Wings or the Plastic Ono Band and thinking, yeah, that's gonna work.