Out of interest, why did no-one notice you were only working two hours a day? Presumably you did the work you were expected to do in that time, but did you not have a manager or co-worker noticing you sitting in the corner reading?
When you're a software engineer, you get a lot of leeway in terms of expected behavior. Especially in silicon valley companies the size of Google, it's easy enough to seem like you're working your ass off, while doing your own thing on the side. It's all about cultivating an image in the beginning and projecting it. People are mostly busy with their own anxieties and career concerns to scrutinize you.