Almost similiar cases happened with me.
My main ID is banned because they said I was involved in a party with bridge, later "Please be informed that your character logs show it was using Bridge Party"

truth: I joined a party via SP, my char level 271, the party leader level 271

1. IF the party is using bridge, how could I know? I joined via asking from Sp
2. As I know the party leader, I ask him and he said something similiar like you, party leader 23x, he is 271, and leader invited lower level char (around180). the leader dc, making him (with 271 the leader)

I think if something like this happened GM need to clarify what bridge is actually
cause as far as I know, bridge is level 271 inviting 204 then 204 inviting 150. the 204 char said yes, the 150 char said yes, then became a party with bridge
if level 231 became leader, inv 271 and 180, how can this be classified as bridge??????