Nobody has proof of anything at the time, because nobody outside of Hello Games really had their hands on it.
The fact remains that he confirmed multiplayer multiple times. Any reasonable person would assume that means that it will be in at launch. The lack of a comment from them stating that the feature had been pulled is them lying either due to their omission of crucial and important information, or because there never was multiplayer and Sean was just going completely nuts.
FYI, that's why developers generally don't put devs in front of camera's and answering interview questions until they're media trained. And if they're going on-air for a TV spot? You bet your ass they're going to get hours of drilling from communications folks specifically to avoid what Sean did throughout the pre-launch campaign.
Compared to the launch version? Literally everything he was talking about in interviews was about the "launch version" of the game that was in development. What the fuck are you going on about "launch version"?
Also, his "response" to player asking him about it on launch day of, "WOW, SO MANY PEOPLE PLAYING! MY MIND IS BLOWN! SO INCREDIBLE!" followed by roughly 6 months of complete silence on that topic, or any other, from himself and his studio despite tons of questions, many about the multiplayer, from fans and media.
Yeah...it does. Because you said it existed, people purchased the game under the impression that it existed, but you neglected to ever tell consumers that anything had changed. So consumers bought it expecting multiplayer and found that they'd been lied to by Sean repeatedly.
No, but if I'm saying that I'll have $100 on December 1 of 2017, and I spend all of 2017 responding to questions about whether or not I would have that $100 on December 1, 2017 confirming that yes, I will, and then December 1, 2017 comes and I only have $80, then no matter what happens I've lied. Doesn't matter if I had to use $20 to save my life, my failure to tell people who believed what I was telling them for 11 months straight means that I spent that time lying.
Except roughly a years worth of interviews where they confirmed a game feature would be in the game at launch, and it was not in there at launch.
*sigh*
I give up. Believe whatever fantasy you want, dude.