Where do you place the burden of proof when someone makes up a story with no evidence and which contradict all legitimate histocal sources - and another comment

Where do you place the burden of proof when someone makes up a story with no evidence and which contradict all legitimate histocal sources - and another comment calls bullshit? The grandparent anecdote is very clearly a work of imagination, while historical sources show that new names were not assigned at Ellis Island, and that Ellis Island officials were multilingual and assigned to immigrant cases based on language.