I just think the old man is a little jealous of Paul because he went through all of the hard work building up the business, and Paul is the one who gets most of the glory. He's a little argry because he is relegated to answering the phones and all of the business aspects while Paul just gets to build bikes. The old man doesn't understand the "creative process". He thinks his scare tactics will grease the wheels, but it doesn't really work. Creativity doesn't come at will.

I'm not sure how much the of the bitching is acted because the way the old man acts like a teddy bear around children.