Look, for all I know, this could be fake. But, when it comes to Steam Inventory, this option is the default: "Keep your Steam Gift inventory private, regardless of your inventory setting above." Go check your profile settings.

This guy has a bunch of games, likes playing them (something like 30 hours played in the past 2 weeks) and already owns Half-Life. What has he got to gain by faking a giveaway for Half-Life 1?