Not true. Take it from someone who is a veterinarian and grew up on a ranch in Oklahoma; a foal is a "baby horse" of either sex, despite what some city slicker may have posted on line. A colt is the equine eqivalent of a child of either sex. There are filly (female) foals and colts, stud colts. There are also adult stud horses (stallions). Of course there are also male humans that think they are, or claim to be "studs"!!
Rachel, I can I assume that your husband did not grow up on a horse farm? Enlightened city folks use different terms for various-aged animals that us dumb country folks don't use. Where I grew up, it was easy to disinguish a city slicker or a drugstore cowboy from the real McCoy! Baby horse folks are obviously city folks.