The busbars existed only as outlines on User.Drawings, a layer DRC ignores, so nothing stopped a part going under a 100 A copper bar. The fix adds a generated board-only footprint per bar with a courtyard KiCad will check plus a copper rule area, though kicad-cli 10.0.0 does not enforce the rule area's own footprint keep-out and a footprint rule flagged 36 parts that were clear of the bars.