In 7.1.5 After Sargeras stabbed Azeroth, Gallywix was the first to know. His cane turned into a piece of Azerite. He knows this because of his previous knowledge from Kezan. "And no one knows about this?" Sylvanas asks. To which Gallywix replies "Don't worry warchief, I've got my boys on it."
"BuT ThE ExPloReRs LeAgUe WaS ThErE FiRsT AnD ThE EvUl HoRdE AtTaCkEd FiRsT!!" Wrong again.
The only mention of Silithus in military context in Elegy were Cordressa's report afterwards and Tyrande being sent there, which happens at the start of 8.0. The events of the 7.3.5 cinematic, which ended with Anduin ordering Shaw to get more SI:7 on Silithus issue happened at the very start of the book. Explorer's League is sent only around ~1/3rd into the book, after Anduin talked with Magni and then consulted what he learned from him with other Alliance leaders. There's nothing to suggest these are the same forces.
So in retrospect, we can already see that the Bilgewater Miners were there first. proceeded with the alliance sending a fleet transporting an army of night elves and Si7 Assassins harassing the workers.
"The crown has ordered SI:7 to infiltrate the goblin mining operation and collect any information we can find on this mysterious new substance. My agents have infiltrated the camp, but the clock is ticking and we need to get our hands on some extracted ore samples fast. In other words, I need someone who can take the direct approach."
And as seen in this quest text in-game, Anduin himself ordered the massacre upon the miners to retrieve the substance. Anduin only wants peace because as we see in the long run, the only ones who benefit from this is the alliance. Saurfang knows in "a Good war" that the Alliance could steamroll the Horde if it wishes, and that gap would only grow bigger as time went on.
So the "You're building war machines, of course we respond." First of all, you didn't even know what the Azerite was or what it was for before you started murdering the miners and analyzing it. Also, so what? The Horde has the right to defend itself. Did you people just forget how Greymane and Rogers annhilated the forsaken fleet at the start of legion with no consequences for their actions? If Anduin can't stop his subjects from attacking the horde, they need to do something to defend theirselves. Prehaps we should as you to dismantle the vindicator or ask Malfurion to go away?