A game can be free without being "free-to-play".
"Free To Play" means the game is free, but that you can (and should) buy additional items in order to improve your abilities/skills to get better chances to win your games by taking adventage on your opponents with those items you buy.
This game is free, but it's not a "free-to-play". You will never find anyone using a 30€ over powered gun on you while you try to kill him with native sucky weapon.
You can support the developpement by pre ordering a steam key (from 5€) as I understood you will have some kind of special medal or so dunno.. They are also looking forward creating a pro league on that game.