Always worth trying the German Docs in Russia site for events in 1940: the situation report for the night of 4/5 June 1940 reports bombs falling on Munich:
https://wwii.germandocsinrussia.org/...inspect/zoom/5
The summary on the first page of the sitrep says that "In the Strasbourg – Basel sector of the front, between 2300 and 0200 hrs. several enemy bombers flew in as far as the Munich – Augsburg – Freidrichshafen area".
Taking Chris's point about the distance and the hours of darkness, could the attackers have been French rather than British?