I think it was strategy on Garret's part!
Think about it: Garret attacking his own main base and seat of power is, certainly, a move that Leonov would never expect....
Seriously though, what are Leonov's strategic options now? I don't see him being the type to just sit still and fight a conventional losing battle. He is now definitely in "high risk" mode, because he has literally nothing to lose.
So, what are his options? If he has some unconventional trick to threaten a planet with destruction, he would likely use it now. (Goodby Pelladon?). Or, what about an armed strike into the Empire . That would likely bring the Sol Empire into the war. True, maybe not on his side, but at this point, he has nothing to lose, so a long shot is preferable to a certain defeat.