The gun and belt were items Danny stole from Orson Randall, a previous Iron Fist. The connection I made was that any weapon chi-charged by a previous Iron Fist, can be used by a subsequent or in Danny's case former Iron Fist. Its not so much he has the Iron Fist back as he can use chi-charged weapons now because he still has the tattoo and there's still a connection of sorts. Like a shortcut. For instance now that Colleen charged her sword I bet Danny can charge that same sword, too. Its like a way to keep Danny from being totally powerless while Colleen is the actual Iron Fist.