I am the Colonel. If I didn't know at least a little about alcohol, and I couldn't handle it myself, it wouldn't be me, right?
And that last part, that's what makes it so hilarious, lol. And why even if it's not true, I wouldn't put it past them to say Alexander was poisoned or died from some other occurrence, if he really wasn't. It would be incredibly embarrassing otherwise for the legendary Alexander.
If there was a cover-up to hide the fact he died of alcohol poisoning, I might buy it. But, bowing to your superior knowledge of alcohol and its effects
, isn't one of the main things about alcohol poisoning the vomiting?
Poison makes more sense to me than alcohol poisoning, as does the worsening of his spinal issues and a disease picked up in the marshes he was traveling in a short time before his falling ill.
His symptoms are interesting. Chills, sweats, exhaustion, high fever, excruciating abdominal pain, being in pain whenever anyone touched him. Except some of the accounts don't have him as having a fever.
All following a banquet with heavy amounts of wine.
There's also the 'his body didn't deteriorate for six days after his death', which could be just building the legend up. God-Kings do not rot. But it could also be indicative of typhoid making him looking dead while he was still barely holding on. *shrug* I've also heard it claimed that some poisons do something similar.
All of this is mostly conjecture until we have his body in the forensic lab. If we ever recover the damn thing. 
It's moments like this I really empathize with the Dalish, desperately trying to find the right clues to the past.
A lot of history is, infuriatingly, the result of accounts written centuries after the fact, using sources we don't have written decades after the fact, which themselves were built off of the memoirs, real and faked, of the people involved.
I want to deploy a CSI team in a TARDIS and find out what killed everyone. 
Also, considering what a Tevinter-style crazy drunken ******* Alexander was in his last years, I really can't blame the Diadochi or his wives or Theo the Stable-boy for poisoning him. 
I'm boring myself at this point with all my ancient death speculation. 
You know what I want from World of Thedas v. II, though?
All of the wonderfully zany exploits and deaths of relatively unimportant Magisters and Archons. Things like Dorian's anecdote about the Archon assassinating someone at a ball and marching off smugly, or the crazier Roman stories, like Caligula having his soldiers hack at waves and take sea-shells as trophies of war for a laugh. (Probably just post-Caligula reign hookum made by a surprisingly creative Roman historian, but Tevinter's got enough lyrium addiction and blood magic for me to buy it for real.)