Meh. It's nit-picking, but I wouldn't say there's anything about OotS goblins that makes them particularly non-human. They're funny-looking, but more funny-looking than a Tuareg tribesman would have looked to a Victorian merchant adventurer? Hell, you can have half-orcs, so they're not even sexually incompatible. By any decent definition they're a human subspecies.
But that's the point: the Goblins don't have to be 'Usually Evil' to behave the way they do towards the humans, so the comic is suggesting that the 'usually evil' label is descriptive of social condition, not base nature.
But then all the goblins we see act like tools towards each other, where human oppression doesn't apply, suggesting that there's something in the 'Usually Evil' label after all, and the goblins are in some way different to humans.
But then the goblins seem to aspire to vaguely human values, suggesting that there's nothing really different about them to justify that 'Usually Evil' label. They're just like humans except all, unaccountably, tools.
Or, at least, all the goblins we've seen have acted pretty much like tools. Who have mostly been the goblin leaders. So maybe 'usually evil' means not well led? Or something else? As I said the Giant's message is not very clear to me yet, but then he does tend to pull surprises out, so there's a possibility he's just getting started.