The Blu-ray is 1.66:1
The red line is the video/TV/DVD framing, the cyan line is the 1.66:1 framing on the Blu-ray (ignore Tigger's tail, they're different frames). The grey area represents the 4:3 frame that would have to be filled out to accommodate the width of the 1.66:1 framing, note that that doesn't mean that the 4:3 version isn't hitting the top or bottom of the open matte, it's just a centered guess.
Here is a section of TFatH that uses a completely different matting than the problematic one from earlier in the film:
