Depends on the person, but yeah, in general asexual people who have sex with romantic partners wouldn't be interested except to please their partner.
And action does not equal orientation. The important factor is sexual attraction. I'd probably ask the guy in your example why exactly he was sleeping with women and whether he might reevaluate his identification, but he might be biromantic and homosexual and also just having sex with a female romantic partner to please her/compromise.