AST-1354: xtensor transition followup

I came across this CreateBuffer() function, which says it has been copied from tIDGPredict and has several other encounters. Prior to the transition to XTensor, this function used to be identical among all these files, but that is no longer the case. This MR fixes that and some typos in the description. The latter is how I found this issue.

Note: after the proposed insertions, they are character-wise identical (except for the function being declared static or not).