In the game, it says in the character report thing or something that moombas recognize people by their blood. Laguna had visited Shumi Village, which is the home of the Moombas. In the desert prison, moomba call him Laguna. Why? They have the same blood. That and Kiros statement in the airship, Laguna having Squall's card, and also Ellone was sent to the orphanage and adopted Squall as her brother probably because she remembered Raine being his mother and Raine raised Ellone so she felt like a sister before the orphanage.