That's what I'm saying.

Even without any OOC knowledge, Shin could put it together that it's a transformative weapon.

A: No sheath visible on her body.
B: Abstract weapon form.
C: Different weapon from before.
D: Previous knowledge of transformative weapons.

I don't honestly see any problem here. In fact I don't understand the question in the first place. Shin was saying that this weapon wasn't the same she was using before, and with no other weapon on her it can be assumed. Shin didn't say that this wasn't her main weapon.