If it’s a company that gets a ton of qualified applicants, it could just be managing applicant flow. You obviously passed the first few screens, the interviewers scored you as “eligible to re-apply”, and just do that in 6 months.

Some companies get so much inbound flow that they can choose between interviewing X again or interviewing X+5000 for a new role. They choose to ensure they look at some fresh candidates by pausing some candidates for a few months.