If he's anything like me I stick my card in the hole in the wall and request money (usually the maximum since I HATE using my card). If it pays out, it pays out. I rarely check the balance.
I'm the same, I always have a rough figure in my head and I don't check the balance too often, but the way the article is written "it showed he was in credit".
If you're normally skint and waiting for money to come through then you're going to check the balance. I'd bet my last breath he knew exactly how much was in his account when he took out that initial �300.