I am a noob so be kind

I converted a video_ts forled to mp4 h264. It wouldn't open with vlc but it did with quicktime. So, as any self-respecting noob would do (), I renamed the file - from xxx.mp4 to xxx.avi and presto, it worked - vlc played the movie just fine.

Can someone kindly throw some technical light on my unexpected success, please.

Thanks,
Eeyaphew