It's possible it was an innocent mistake, and she didn't allow that mistake to surface. Maybe he mistook her for someone he'd already spoken with. Maybe the recruiter he talked to was named Rachel and/or had a similar voice, or even a recruiter at a different company, and he got confused.
Confusions like that would have easily surfaced if she had asked "What made you to believe this isn't the technical interview?", but instead she played the part of a less technical recruiter trying to give a technical interview.
As the candidate, that's a curveball you should be able to handle and you should still act professionally.
If I went to interview with some small company and the technical interviewer didn't seem to know what they were doing, that would certainly be a mark against the company in my book. If they extended an offer, I might decide not to take the job.
But things can happen. What if the real technical interviewer had a sudden crisis come up and someone else without much experience was substituting in? If you do a good job they may be impressed with your communication skills on technical issues when talking to less technical employees. Maybe you'd get a further interview with the more technical person since you did a good job in that accidental circumstance.
There are quite a few people here saying she was unprofessional for handling things that way, that she should have cut the interview short. If he thought company was acting unprofessionally, he could have just cut the interview short, saying he didn't think it would be a fit.
For all we know, as soon as the interview started he made up his mind and stopped trying.
Confusions like that would have easily surfaced if she had asked "What made you to believe this isn't the technical interview?", but instead she played the part of a less technical recruiter trying to give a technical interview.