The Rambam writes that a nochri who strikes a yisrael is chayav misa, but is not killed -- i.e. it is a chiyuv misa b'ydei shamayim (Melachim 10:6). The Rambam himself (Chovel u'Mazik 5:3) cites the gemara's proof: in our parsha Moshe strikes down the Mitzri who was hitting a yisrael. This is a very strange proof for a chiyuv misa b'ydei shamayim considering that Moshe actually killed the Mitzri in question!
In the Igros haGR"ID there is a shtickel torah that R' Ahron Soloveitchik said on this when he was 10 years old (!) Rashi writes that Moshe Rabeinu killed the Mitzri using the shem hameforash. R' Ahron suggested that this method of misa is at best a gerama, not a true action, and therefore does not constitute a ma'aseh of misas beis din. His proof: the Ritva writes that asking someone to commit murder is a gerama, not a real act of murder. We see that speech is not the same as action; QED that in our case as well, killing through speech is not the same as an act of misas beis din.
R' Moshe Soloveitchik wrote this shtickel to the Rav in a letter along with a he'ora of his own, and the Rav responded with a number of additional observations. I feel sorry for R' Ahron, who probably worked pretty hard on saying his chiddush, something any 10 year old could be proud of, yet it gets swallowed up in the complex give and take between the Rav and his father. The Rav rejected the proof from the Ritva, arguing that there is a difference between asking someone else to take action (=gerama) and a case where one's own words produce an effect, which is itself equivalent to action. The Rav also noted in passing that the chiyuv misa b'ydei shamayim in the case of murder is unique. With respect to other chiyuvei misa b'ydei shamayim, e.g. a zar who eats terumah, there is no obligation except k'lapei shemaya; however, with respect to hitting, there is real chiyuv misas beis din that at least should theoretically be carried out, but for technical reasons is transformed into a lesser punishment b'ydei shamayim. Finally, the Rav noted that this is not the only case of misa b'ydei shamayim given to a nochri. Similar chiyuvim exist for a nochri learning Torah, keeping Shabbos, and other cases. Although any violation of the 7 mitzvos is punishable by misas beis din, apparently these other violations, including striking a yisrael, are categorically different. The question is why, but I'm short of time, so we'll leave that discussion for another time.