Gotta love those first week losses. Along with some fat loss that first week, there's excess water weight shed as well, thus the large loss. More then likely, you will not see a number like that again and again, but you never know.
Weight loss is not linear. Even if we could possibly replicate the same thing, food wise and exercise 4 weeks in a row, you would most likely get 4 different results.
You're off to a GREAT start. Just keep at it. Keep on going.