Or HaChaim on Exodus 18:12/אור החיים על שמות י״ח:י״ב

1 ויקח יתרו… עולה וזבחים, Yitro took total offerings and meat offerings, etc. Yitro was clever in offering numerous peace offerings. He did this in order to be able to play host to many Jewish dignitaries. This is the reason it does not say: "he invited Aaron and the elders," but "Aaron and the elders came to eat with Moses' father-in-law before the Lord." They did not need to await an invitation because the quantity of Yitro's offerings spoke for itself. He certainly would not have allowed all this meat to go to waste as it would have been forbidden to do so. The elders honoured Yitro by joining him without a personal invitation being extended to them.