Or HaChaim on Exodus 18:3/אור החיים על שמות י״ח:ג׳

1 שם האחד גרשם, the name of the one was Gershom, etc. Although the reason Moses named this son Gershom has already been mentioned in Exodus 2,22, it had to be repeated here in order to inform us that we are talking about the same son already mentioned in chapter 2 (though this may have been 60 years earlier) and not another son (by the same name but born of a different mother).

2Furthermore, the Torah may have had to mention that the reason was not that Yitro had expelled Moses from his home. While it is true that Moses said: "I used to be a stranger in a strange country" (obviously not referring to his being expelled by Yitro), he may have phrased it thus so that Yitro should not hear that he had referred to expulsion by him. The Torah repeats here once more that the reason for Gershom's name was Moses' grateful acknowledgement of having prospered as a fugitive in a strange land.