In context, with Trump denying the DNC hack was Russia trying to help Trump out, yes, this one can be seen as a very obvious joke. Just because he frequently makes horrific statements doesn't mean he doesn't occasionally also make jokes.
"Obvious"? How can you possibly tell the difference? Please let us know - what's the tell here? When you layer on the fact that Trump frequently contradicts what he has said (sometimes in the same sentence), and frequently denies saying things that are thoroughly documented that he said (video recordings are a thing he seems unaware of) how can one tell he means anything he says? Maybe his whole campaign is a joke?