AMD performs extremely well in that specific game, Ashes, due to vendor-specific optimizations and dramatically superior asynchonous compute performance. So far that hasn't translated to better performance in any actual games. AMD also performs very well in DOOM with Vulkan for the same reasons.
The RX-480 can't come close to the GTX1080 even in those two games, but I can easily see Vega beating it. But only in those specific games.
The PCgamer article estimated performance beating a 1080 based purely on AMD's numbers, which are usually bullshit (AMD exaggerates regularly), while the Techreport article used actual performance in a videogame.