Got offered a job then told they are going to conduct more interviews

Went to an interview and was called back within an hour by the recruiter to offer me the job at a fairly large company. Was told I'd be sent an offer letter by night. 3 days go by of me not getting the offer letter then am finally told they are going to do some more interviews and let me know a week later. Idk if it was miscommunication between the recruiter and owners or they changed their mind but the entire situation just seems super unprofessional. Major red flag but im desperate for a job out of college.