That can't be true, minecraft already had multiplayer in 2009. He didn't make it intentionally painful and never said anything like that. I remember there being huge issues with multiplayer but that was mostly because of bad architecture, not intentional.
Correct, I don't think he hesitated even a little bit on adding multiplayer support. The very first announcement of Minecraft's existence mentioned two planned game modes (fortress and team survival) that would require multiplayer and that all gamemodes would support it https://forums.tigsource.com/index.php?topic=6273.0
yep, just to add to that I remember there was a big deal to rearchitect the entire engine to use a client-server architecture even when running singleplayer. This also enabled the "Open to LAN" feature in which you can start a server from your singleplayer world with a single click.