כָּל אֲשֶׁר עָשָׂה אֱ־לֹהִים לְמֹשֶׁה וּלְיִשְׂרָאֵל עַמּוֹ
Why are they separate? Did something happen to one that did not happen to the other?
This where the Medrash Learns that Moshe alone was equal to all of Klal Yisroel .
Ramban: Yisro heard about the wonders that H' did for Moishe personally, ie the H' dealt kindly and beneficently with him in that he always came to Pharaoh with his demands without fearing him, and that he brought the plagues on Pharoah without retribution
The CHIDA in Rosh David answers that Yisro Had worshiped Idols all theses years was Unsure he could still become a convert. Then he heard of Moshe Accepting of the Eruv Rav and Hashem agreed to accept them and that the Jews themselves worshiped Idols. So it works like this:
כָּל אֲשֶׁר עָשָׂה אֱ־לֹהִים לְמֹשֶׁה:That Moshe accepted the EREV RAV and Hashem agreed to allow them in. וּלְיִשְׂרָאֵל עַמּוֹ that they themselves where Idol Worshipers and Hashem accepted them too He heard this He knew he could come and join also.