adjective

resulting from a coincidence; happening by chance.

any resemblance between their reports is purely coincidental

accidental,chance,occurring by chance/accident,fortuitous,adventitious,fluky,casual,serendipitous,random,aleatory,unexpected,unforeseen,unanticipated,unforeseeable,unlooked-for,unintentional,unintended,inadvertent,involuntary,unplanned,unpremeditated,unthinking,unmeant