Using SSH to backup your SQL file doens't specifically compress the database, the --opt command optimizes the database and clears the overhead on each table. While it may appear to be smaller, the database is actually the same size, without the overhead.
As for Site5, they actually do use CPanel, it is simply a skinned version of CPanel which is rebranded. They have indeed added their own features, such as FlashBack and such services, however it's easy to see they still use a rebranded version of CPanel

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