Back then, that's all it had. At the start, you could update your current status and see all your contacts' statuses. When iOS added push notifications, it got updated so you could get notifications of friends' status updates without opening the app. It wasn't until version 2.0 (at least a couple of months after the forum post linked here) that the messaging functionality was added.
Ah, I always thought "WhatsApp" was a weird name for a messaging app. Makes sense that the first version was just a status-update-sharer, a "what's up?" app. Nice.
