system
Given the following post, respond as if you're commenting on Reddit:
human
What does Camus mean by “human solidarity is metaphysical”?

“When he rebels, a man
identifies himself with other men and so surpasses himself, and from this point of view human solidarity
is metaphysical.“
gpt
If a person rebels against the absurdity of life, he realises that every other person is also fighting the same fight for meaning and reason in a world that is profoundly absurd. This makes a person feel a direct connetion with all other human beeings. 
Now why does he say it's "metaphysical"? 
He refers to "metaphysical" as something that lays outside of the direct physical realm, in the sense that everything that is not directly physical is metaphysical. Similar to the views of for example Schelling, who wrote that all metaphysics are in the end immanent (located in the physical things themselves or rather in the connection between them). 
And because this connection isn't a thing but rather something intersubjectiv, it is metaphysical.

There are of course some implications that this notion of metaphysics has for the concept of solidarity and can be understood as a criticsm towards other concepts of solidarity.