Ok so, I have 2 issues with this;
1. I would've hoped the reveal of him not knowing how he made the elixir actually came from him researching something else, maybe increasing mana compacity or something like that, him drinking it, realizing it didn't work, and throw away all the notes thinking it was a failure just tp realize a hundred years later what he actually had created, not what we were given because that's just stupid..." Some unknown liquid" Really? If an unknown liquid fell into your food, THAN WHY DID YOU STILL EAT THE FREAKING CAKE?
2. The dumbest thing he has done here is keep it a secret that there is someone behind the attack, why would you do that when you knew that WHO KNOWS HOW MANY LIVES ARE IN DANGER BECAUSE THAT PERSON WANTS TO DESTROY THE NATION! IT makes no sense especially from a moderately intelligent mc.