TGM Plugin Activation is a PHP library that allows you to easily require or recommend plugins for your WordPress themes (and plugins). It allows your users to install, update and even automatically activate plugins in singular or bulk fashion using native WordPress classes, functions and interfaces. You can reference bundled plugins, plugins from the WordPress Plugin Repository or even plugins hosted elsewhere on the internet.
This is unrelated to TGMPA - these styles comes from WP core and as TGMPA does not register a page when there is nothing to show, this is not something which IMHO should be solved in TGMPA.
Apparently, when there is nothing else to install, the header and footer of the table are empty but still take space (are visible):
I think these should disappear when there are no plugins to install as there is nothing inside them and only break the page aesthetically.