I agree. I had an interviewer read all 6 of my LOR in front of me and it turned out my one anthropology professor wrote the best LOR of the bunch! All the science profs. just wrote a paragraph... Definitely hit up those non-science because they write great LOR's
First off, I think if you elaborated a little bit more, this could belong in that "awkward interview moments" thread

I'm very surprised that your interviewer did that!
I am not surprised, however, that your anthro prof wrote you a good rec. I got a rec from a prof who I did a year-long philosophy seminar course with - very small, discussion based, tons of participation required. Turns out, he loved me and I didn't even know it. When I asked for a letter, he told me that I out shined the other students by a long shot
😛 and that he'd be glad to write for me. He also said - and this is the huge part - that due to the 'pecking order' of academia, and the fact that he was a post doctoral fellow rather than a prof,
he went out of his way to write an extra glowing and descriptive letter 😱 because he thought it was the only way to compensate for his lack of clout
😀. I think that was an uninformed decision, as I doubt any adcom cares whether he's an assistant or associate prof or whatever, but I didn't object

.
By contrast, I've done very well in competitive science courses whose profs ended up knowing my name despite having 400+ students. When I've approached them for med school recs, I've gotten responses like "well, I can do it, but all I'm really gonna say is that you got an A and I saw you in office hours"
In short, humanities profs are sometimes your best bet!