Nah. Even if it's hetero, it's probably not straight. Straightness is similar to whiteness; simply a term to say "you're normal and deserving of respect." It's a normal word, not simply a descriptive one.

Dating a nonbinary person as a binary person is definitionally hetero, but hard to call straight. An agender person and a bigender person would totally be het, but totally not be straight. If it's not a relationship between 2 monogamous, cishet people assigned opposite sexes at birth, it's weird and unnatural.

Bigots can literally gatekeep straightness from a cishet woman dating a cisbi man. It's like a tainting of her for being with a queer person, even if neither she nor the relationship is queer. It doesn't matter if they're monogamous for life; it's one drop of queerness poisoning their ability to be normal. They'd need to hide his true orientation.