I got a similar feeling when Amazon once reached out to me.
I got a recruiter email and I wasn't super interested in working there, but was a little curious, so I responded. They wouldn't tell me what project it was or what I would be doing exactly, but said that once I was brought in for a full interview loop I'd sign an NDA and they'd tell me all about it. I said I wouldn't mind having a conversation on the phone just to learn what I could from the hiring manager since I wasn't comfortable spending time on a phone screen if I wasn't even interested in the job or the project. The recruiter set me up with a call with somebody on the team.
So I had a phone conversation with somebody on the team, expecting it would be an informal chat about what they do and what they're looking for, but after about 20 minutes they started asking me design and behavioral questions (i.e. given situation X, tell us what you would do). I was really annoyed because I just wanted to get a feel for what the role entailed and what they were looking for, but they turned into a sort of interrogation to see if I had what it takes to join at all.
I was already starting to look for a new job at the time and was familiar with Amazon's principles, so was sort of prepared for it and I answered all their questions quite well, and they seemed happy. I kept trying to steer it back to things I wanted to know, however, but it was hard.
Overall, I felt like the call was a waste of my time since I didn't learn anything about the job. I guess you could say it saved me time later since I decided not to respond to any future emails that other recruiters sent me.