I don't fault the guy for the arbitrage, just for not fulfilling the contract. It would be about equally unethical if he were doing the great work himself and got bored and wandered away.
It's in most standard employee contracts that employees won't disclose confidential information for reasons like this.
Contractors are expected to be shorter term and change tasking if new opportunities arise, even for a short time.
If both parties enter into a deal then it's fine, if one is misrepresenting themselves it's not.
How quaint.
/s
When an employee does it without informing the employer or signing an agreement that holds the contractor to the same standards as the employee the chain of trust, transparency and accountability is broken.
Well, it's entrepreneurial, but he's almost certainly also violating all kinds of employment stipulations and policies he's formally agreed to (security, privacy, etc.)