Yeah, this isn’t really true either. When shown clips of different people having sex, hetero men physically responded to clips of men and women, and gay men responded to clips of guys together. Women responded to anything and everything sexual, including monkeys fucking. The sensors were on their genitals, so it wasn’t something that could be faked.
It’s true that women want to feel safe when engaged in sex because being a woman is so inherently dangerous and sex is a pretty vulnerable thing, so women are more likely to feel sexually responsive when there is a real connection going on, but if it were safe, both physically and from a social censorship perspective, it’s pretty likely that women would be just as into casual sex as men.