Most Helpful Guy
It really depends on the guy. Studies have shown guys forget more frequently than women do, and both are bad about dates. He probably just remembers that her birthday is an important date, and if they were along together it's even harder.
If he was doing stuff with her, the fact it's her birthday would be in the front of his mind, so I doubt that he's talking to her right now. It just doesn't seem to add up. He's probably just bad at remembering stuff, and doesn't have any tricks to remember your date yet.