Bullshit, that's not what happened at Nagashino.
You can't penetrate Damascus steel with blackpowder muskets, the bullets would ricochet off of it because they're pellets.
The reason Nobunaga was able to take out the forces at Nagashino was because it was a Calvary charge, so they shot the horses. Plus Samurai Armor wasn't made of fucking steel, but bamboo, and their ranks also had peasants and other lighter units.
Also, if he had access to explosives, why didn't he equip his men with that to begin with instead of having to lose the fight?
It makes no goddamn sense.