The issue is that only very old channels (e.g. "pewdiepie" or "pgatour") can be found using the "channel method. This means that for most search requests for channel name, this site uses the "search" method, which uses 100x more quote units. Hopefully Google will change this in the future so that this site can get more free quota. If you get a 403 error, now you know why.
For any inquires email ytstat [at] gmx.com