There's an unbelievable amount of plot holes in fallout that are a lot easier to explain if you consider some folks in the post-post-apocalypse might be full of shit.
There's also a woman who at least claimed to be a Jet addict since before the kid was even born in the same game. Is it possible her brain was just fried and she was projecting her current fix over all her past problems? Maybe. But whether it was the original intention at the time or a retcon, at this point he must have been bullshitting to some degree. Most generous possible reading with current available facts is something like "discovered a process to mass produce an existing but potentially rare prewar Chem with postwar tech and claimed to have done the whole thing"
Hi 'how could jet have been found in vault 95 during the events of fallout 4 in 2287 after being placed there by vault-tec before the war when jet wasn't even made until 2242 during the events of fallout 2 by a kid in new reno the drug couldn't have been put in a pre-war vault if it was made 165 years after the great war'
Myron got sex slaves, caps and fame for cooking improved Jet on behalf of a post-apocalyptic gangster crime family. Of course he’s going to lie or inflate his intelligence to god like genius