Did some Zappreuder analysis of this film.
Note this image - check out the shadow left by the tree noted by the green arrow.
Now, ASSUMING both referees are on the goal line, we can draw an approximate goal line, which cuts right above the shadow landmark.
So, it looks like this is VERY close to the goal line (not 5 yds in) and the referees probably weren't positive the ball crossed the plain, so they let it go.
Note: the camera may have moved a little from it's original position on about the 7 to about the 4, so the parallax/angle may be off a little.
How's that for analysis?