% of frame that is white was throwing your in camera meter off. It was probably trying to properly expose the entire frame. Set your camera to spot metering, or move camera in till the little guy mostly fills your screen, make note of the readings and switch to manual and replicate the settings when you pull back out.

While a hand held meter does this by its nature, (holding the meter right in front of your subject when poping your lighting or existing ambient light), the meters in the camera are a huge part of and cameras ability to properly expose any image. I think Nikon/Canon/Etc., would have issue with saying their in camera meters don't work well, their job is pretty simple after all. It's just returning what it "sees", it's up to you to show it what you want. And in fact a hand held won't help much if you don't use it right, but no argument about what one can do!

What a hand held meter can do that your camera can't easily is figure out what individual light source(s) are emitting, so you can figure out an adjustment to solve a problem or to set up. It is a valuable tool in a professionals portrait gear.