It's not really surprising that Vox would publish something like this.
EDIT: To clarify, arguing about this is a complete waste of time. Democrats will see the results of these special elections as proof that 2018 will be a very good year for them or even a wave, while most Republicans won't. We won't know who is right until the election actually happens.
This about sums it up. I am content to wait until November 2018 to see what actually happens; folks until then are just going to go back and forth insisting that this or that will happen, with this or that typically being what is politically convenient to the speaker.