Founders selling a small percentage of their stock as part of a (usually late) financing round is pretty common. It's in the investors interest to see that the founders are focused on growth and not lured by an exit at an unattractive multiple. Letting founders take cash off the table by selling a small percentage of their stock as part of a late financing round keeps the founder focused on growth instead of creating liquidity for themselves. Secondly, capital gains tax on a stock sale is much lower than income tax that would be garnered by paying yourself a bigger salary.

A VC who has participated in an early round also often sells some stock in a late round to hedge their risk.