In 9:10 the Passuk tells us the Jews killed the 10 sons of Haman. Rashi says it is brought down in Seder Olam that these 10 sons of Haman had disparaged Israel, when Koresh had allowed the jews to return and begin rebuilding the Temple, then Ahashverosh took over and Haman came to power and he wrote accusations against the jews to stop them from returning and rebuilding.
The Megilla is indicating that they are singled out here as having been slain by the jews, despite many other people having been killed as well, specifically to tell us that they were slain as retribution for their false accusations against the jews and Israel.
Gods got our back, You want to mess with us, you are also messing with God. he particularly takes offense at those who disparage His nation and country. Do so at your own risk.