From the research I’ve done, the Midianites were descended from Abraham through Keturah (Gen 25:2) and must have had traditions of Abraham’s God.
Adam Clarke writes in his commentary, “Some think that Jethro was now converted to the true God; but it is very probable that he enjoyed this blessing before he knew any thing of Moses, for it is not likely that Moses would have entered into an alliance with this family had they been heathens. Jethro no doubt had the true patriarchal religion.”
And Matthew Henry writes in his commentary, “The confirmation and improvement of his faith: Now know I; he knew it before, but now he knew it better; his faith great up to a full assurance, upon this fresh evidence. Those obstinately shut their eyes against the clearest light who do not know that the Lord is greater than all gods.”
And John Gill writes, “He knew the Lord before, and that he was the only true God, and greater than all that were so called; but now he had a fresh instance of it, a clear proof and demonstration of it, and so more plainly and fully knew it, and was assured of it, that he was greater than all the idols of the Gentiles, and particularly than the gods of the Egyptians;”
To say he was a pagan priest just doesn’t make sense to me considering the verse after Exo 18:11.
Exo 18:12 And Jethro, Moses' father-in-law, took a burnt offering and sacrifices for God: and Aaron came, and all the elders of Israel, to eat bread with Moses' father-in-law before God.
For how would he have known to make a burnt offering and sacrifices for God if he was a pagan priest? As I stated above he must have known the traditions of Abraham’s God.
In Christ, 1Christianwarrior316