Staffing Agency

I wasn't sure what to make of this - if anyone has any advice/experience, it would be appreciated.

I interviewed at a company for an internship a few days ago, and haven't heard anything back from them directly. However, "Kelly Services with [Company]" called me today to begin the onboarding process. I was confused, and had to ask if I had been hired, since I hadn't heard from anyone at the company that interviewed me. They told me I had been selected for the position, and sent me emails for the process. My interviewer never mentioned Kelly Services, so I emailed him to ask if this was the hiring process. I can't find much online relating Kelly Services to the company I interviewed at. I applied to this job on my university's job website, so I'm not sure how their service would've received my information, if not from the company. Is this legit? And should I wait to hear back from my interviewer before I fill anything out?

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