I think it’s healthy to observe your partners reaction to things. Especially when it comes to things that are quite important for a long term relationship, like their thoughts about gender roles. If you organically went to see the movie and your partner is clearly displaying red flags from it, then that’s just good (not the red flags but that you now know).
I guess the trickery of going to assess them specifically can be seen as a asshole move. But I think it’s a good move compared to alternatives ^^