Where in the world are you getting it from that the name of the street made it ok to bomb? He's saying that he learned of the street because the Russians bombing it was newsworthy given that it killed 20 people. Then what followed from him learning that the street exists with the name Bandera, was him thinking that maybe there could be some support for Nazis still remaining in Ukraine. Similar to how seeing a street named after a Confederate fighter would make someone think that maybe there's still some love for the Confederacy in the US (which is actually accurate!)