There's at least one other Japanese movie which features a bunch of aliens holding a conference at the start;
Evil Brain from Outer Space. Apparently this film was put together from parts of a Japanese serial, and there were at least three others in the series (which I never saw). It's possible that they tacked the alien conference scene at the start of all four films to explain how the hero ended up on Earth. Here's a review of two packages which contain two films each;
Starman Volumes 1 & 2The one I recall seeing had the creatures with the fangs and weird Mickey Mouse ears.