I just added a new contact to my iPhone. When I look at the contact page there's a FaceTime icon (Under, next to that person's phone number). Does that mean that this person has an iPhone?
Broadly speaking, the presence of FaceTime row in a contact's screen means that the contact is registered with FaceTime service, which by extension means that the person uses/used one or more Apple products (Mac, iPhone, iPad, iPod), which support FaceTime calling.
The person may or may not have an iPhone. Person's Apple ID is used to register with FaceTime. An email address is required to create an Apple ID. The mobile number gets registered/linked to the Apple ID if used with an iPhone where the user has logged in with his Apple ID.