It's all about the conclusion:
Whoever created the signature of the message was definitely in possession of the private key that Hal Finney had in use at the beginning of 2009. However, it can be ruled out that this signature was actually created in 2009.
Furthermore, it was already known before that this private key was still in use after Hal Finney's death († 2014) (for example this transaction from 2017 proves this).
Fact is, it is not known who currently holds possession of this key, nor how they came into possession of it and I refrain from useless speculations on this matter.
