Shortly after sunset on June 18, 1178, five monks from Canterbury reported seeing what they described as two horns of light on the shaded part of the moon. Modern theories predict that there would a plume of molten matter rising up from the surface of the moon, which is consistent with the monks' description. In addition, the location they recorded fits in well with Bruno's location. Additional evidence of Bruno's youngness is its spectacular ray system: Because micrometeorites constantly rain down, they kick up enough dust to quickly (in geological terms) erode a ray system. So there is probably enough circumstantial evidence to hold that Giordano Bruno was formed during human history.
However, the question of Bruno's age is not that simple. The impact creating the 22km wide crater would have kicked up enough debris to make a meteor storm one Earth with ~50000 meteors hourly for up to a week. There is no way the entire population of the planet could possibly have missed the greatest fireworks show in history! This is such a major objection that few astronomers still believe Bruno formed then.
All this begs the question of what did the monks see? An alternative theory holds that the monks just happened to be in the right place at the right time to see an exploding meteor coming at them and aligned with the Moon. Only a small area in Britain would have the perfect geometry to make it look like it was on the Moon.