Well; what an amazing coincidence that we happen to be in the power armor business? Power armor that has thick armor plates made from super-materials that are likely both highly thermally conductive (spread the heat load over a larger area) and possessing of a high heat capacity (harder to heat in the first place).Huh, you just invalidated all personal kinetic shields....whoops?
To be fair the alien perspective isn't exactly wrong. There is a reason the rest of the galaxy call it the Relay 314 Incident (only humans call it the First Contact War). Humanity was violating interstellar law by attempting to open a Relay and the Turians were fulfilling their duty as space cops by stopping them. Then we retaliated and killed the space cops which resulted in space SWAT being deployed at which we (after some struggle) overwhelmed them and forced a retreat. So the space national guard was called in to suppress these dangerous criminals only for the politicians (IE: Asari) to get involved and deescalate the situation.The way this was worded, it sounds like the rest of the galaxy thinks that the humans attacked first. Like, the Turian sent a diplomatic ship or something, and the humans shot it down. And now you're telling me it's all the fault of Turian Boomers.
So humanity starts off being seen as a race of cop killers and criminals. Then we quickly expand and start making wild claims on space despite our tiny population. Seriously Alliance Territory is the same size as Inner Council Space and we are also pushing to claim the Attican Traverse which is somewhat larger then our already claimed territory. All the while the Alliance is building Dreadnoughts as fast as it can afford and pushing the Batarians out of space that was unofficially considered theirs to claim in due time. We are also stirring up the Terminus Systems by harshly punishing pirate raids. Sure the Massacre at Torfan hasn't, and likely won't, happened here but similar things likely have.
Combine all that with the clear xenophobia plenty of humans demonstrate and it is easy to see how such a reputation could form.