I believe Snowden needs to be pardoned. He made the Public aware of the shady things that are done in its name. So the Public needs to pardon Snowden for being a whistleblower and this can be voiced through the President, who is supposed to be the ultimate voice representing the Public and its interests.
However, Trumps motivations for doing anything have been fickle and marred in short-term political or personal popularity gain, sometimes to the detriment of the very thing he is supporting.
So supporting a pardon for Snowden is great but the reasons for doing so are really not clear and -as usual- not articulated in any sensible and reasonable way.
Maybe I'm wrong but this looks more like a political diversion to me, maybe a way to divert the outrage when he pardonned Stone -clearly a shady character if there was one- or just keep the news busy for a while.