The book I referred to on this is the Grammar of Septuagint Greek,
Conybeare & Stock, 1995, Hendrickson Publishers, page 58. The verse used
is Deuteronomy 15:10, LXX.
The "vernacular" premise may not be ruled out. The genius of the writer
may well reflect on the personality of Jesus Christ to use a phrase that
transcends literary finesse! Talk about a quotation verbatim.
I would paraphrase what Jesus Christ said as, "...is not ...although you
claim him as yours ... husband ..." It is a case of what the Law views of
the relationship and what she views of the relationship! On legal grounds
not her husband, but she claims him to be!