My personal hypothesis is that insiders saw a clip of Incineroar running around and interacting with some kind of Minecraft thing. Be it a creeper, a Minecraft stage, a Minecraft cat as part of his trailer, whatever. That's where Verg got their "Incineroar and Minecraft representation" information.
A lot of people saw this video, so they are dead certain that Incineroar is in the game and his absence on the banner means it's fake. However, it doesn't match up with the current "climate" of Ultimate in my honest opinion: while Incineroar is one of the more popular pokemon from that generation, it's not a "meme pick" like most of the roster has been so far which caters to hardcore fans. I can absolutely see Incineroar either being an AT that people thought was a character, a really developed Pokeball summon, or just an originally planned character that got shuffled to DLC (because they know enough people will buy any Pokemon character.)
I'm almost 99% sure that people are putting their reputation on the line over the wrestle cat because they saw him in action.