I have been on these forums for a while and to my recollection it is quite rare for followers of the "Aiki" or "Internal Power" to agree on anything that in some way pins down their practice. On the discussions I followed, I have never seen Aiki/IP described as "unbendable body".
It's entirely my own thought. I am new to the whole IP thing and am trying to make sense of it in terms that I am already familiar with. It is most interesting to me that some aspects of it exist to a degree in some styles of Aikido. I definitely felt this for the brief time I practiced with a Renshinkai group.