The argument of (1) doesn't really have anything to do with humans or antromorphising. We're not even discussing AGI, we're just talking about the property of "thinking".
If somebody claims "computers can't do X, hence they can't think".
A valid counter argument is "humans can't do X either, but they can think."
It's not important for the rebuttal that we used humans. Just that there exists entities that don't have property X, but are able to think. This shows X is not required for our definition of "thinking".
Certainly many cultures and religions believe in some flavor of intelligent design, but you could argue that if the natural world (for what we generally regard as "the natural world") is created by the same entity or entities that created humans, that doesn't make humans artificial. Ignoring the metaphysical (souls and such) I'm struggling to think of a culture that believes the origin of humans isn't shared by the world.
In this case, I was thinking of unusual beliefs like aliens creating humans or humans appearing abruptly from an external source such as through panspermia.
If somebody claims "computers can't do X, hence they can't think". A valid counter argument is "humans can't do X either, but they can think."
It's not important for the rebuttal that we used humans. Just that there exists entities that don't have property X, but are able to think. This shows X is not required for our definition of "thinking".