Match Sequence settings means just that: it uses the preview codec used in the sequence.
In this case its the mpeg Preview codec with lesser quality.
Best is not to use this setting. Its used for a quick output.
Just choose one of the H.264: you can tweak the settings if you like.
There is still something I don't get, if "match sequence settings" creates a "lesser quality" file how come the size of this file is 3 times bigger than the more quality H.264 file?
That is because of the codec: I frame only mpeg.
H.264 is much more efficient.
Thank u Ann for making the picture much more understandable