If you had gone to the police they may have tested you for drugs, found something in your system and you would be in the Aguascalientes jail singing " Oh Canada"
Never leave your drink unattended or accept a drink from a stranger.
I've accepted many drinks in Mexico, but different circumstances than what you've described. Often during calendas (processions) that circulate through city streets an organizer will carry a bottle of mezcal which is poured liberally into small plastic (disposable) containers, or cane (reusable) containers, for those who've joined in, or even bystanders. I consider these drinks safe as everyone drinks from the same bottle.
Reading the entirety of your original post, my feeling is that the most likely scenario is that you had your pocket picked by someone other than your new-found friend(s). Large events that are scheduled well in advance, are pickpocket magnets. I don’t know about Mexico, but in India some of the best pickpockets are kids.
I put the chances of you having been drugged at 50-50. Just as likely, your body was worn down from having stayed up partying until 6 in the morning and this was affecting the way you felt. Your friend didn’t have the same experience of being drugged.
“Do I punch him in the face right now? I’m bigger than him, but still disoriented, and he probably doesn’t even have my phone on him anyway…”
That would have been a bad mistake. Either you would have punched an innocent person, or you would have punched a guilty person. If the latter, there would have been a good chance that you would then have seen his friends coming out of the crowd to set upon you. In any event, a loose-loose reaction.
Holy mother of shaggy dogs... that entire tale could've been told in one paragraph, two if you wanted to be long-winded about it. "A 2000-word story" indeed. Shorter version: "Went to a Mexican festival and was most likely pickpocketed after getting dry mouth from drinking so much."
I agree that this is probably just someone's stab at forum fiction, but if this is actually true, I would say to try to reorient and take a new tack... the way it's written does sound like someone who gives off an "easy target" vibe from miles away.

Have always travel insurance and always make a police report. Stay off of face book and never let anyone know you have a phone. In Mexico I use a cheap phone from walmart to make any local calls.
Yes I may be a little paranoid...I would say "security conscious". But there are too many shady détails in this story, some that I did not mention here. This Armando guy disappearing constantly for no reason, especially after the phone was gone. The pills they offered us. The Facebook profile of Lex, which I saw the next morning: "joined march 2017", "from New York" (he had said San Francisco), "studied at the London School of Economics", zero friends, no full picture of his face anywhere. And yes, there is a lot you can learn from looking at a Facebook profile, the kind of stuff (mother's maiden name, city of origin, pets, etc) that would help you get into a social media or banking account trough "security questions", for instance. You already seem to believe I'm a little crazy, so I'll also say this: it could also tell them who to contact for ransom.
I don't think you were paranoid, but rather as you say 'security conscious'. I can say that I've experienced almost no attempted scams in Mexico thus far, and by comparison in India and in Bangkok, Thailand scams (or attempts at them) are encountered quite frequently. There have been numerous cases of drugging in India, some that have even caused death.
I can't imagine putting anything on a Facebook account like your mother's maiden name...same on a phone or pen drive that could be stolen.
I think your safety conscious ways will probably serve you well as you travel.