A movie file has a container, which is the format that wraps the whole thing, usually indicated by the file extension. Each video or audio stream within the movie file has a codec, which is the format in which the stream’s data is encoded.
A movie player will look at the file extension, the container, and the codec to decide how to play the movie file. Each container is compatible with some particular set of codecs, so the movie player has some expectation about what codecs to look for when it sees the container type. However, these are not always clearly specified, and support varies from one movie player to another as they all use different heuristics.
The video metadata you posted shows that the problematic video’s container is MPEG-4 and its video codec is AVC, which is odd since the file extension .mpg implies MPEG-1 or MPEG-2. Presumably whichever of Vuo’s two movie player libraries — FFmpeg or AVFoundation — was selected to play the file got confused by the mismatched combination of the .mpg file extension and the actual MPEG-4 container format.
Since this seems like a rare case — not affecting a wide range of .mpg files, but only those which are actually MPEG-4 in disguise — and since the workaround is simple, we’re going to close this bug report in order to focus on higher priorities for development.