Just as an aside, it is my feeling that the evidence against Paul being the writer of 2 Thess, is much heavier than anything claimed to support his authorship.
As to "all scripture........" it is my thought that Paul would not just have rated the Tanakh, the Hebrew Bible as we call it, as "Inspired" but would more than likely have given equal weight to the thoughts of earlier Rabbis not contained within that "Bible", we are shown in the Gospels that Jesus did just that, his " Golden Rule" being a direct rip off of the words of Rabbi Hillel.
But as pointed out above, these writings were all he would have had, the Gospels being written years after his death, and he certainly did not think of his own writings as "inspired of god".
But of course the " all Scripture......." quote comes from the pen of a writer pretending to be Paul, Prof Bart Ehrmann calls these Letters not just pseudepigraphy, but " Fakes".