Smith actually makes some good points in that video, at least if you can look past the vague threats. He doesn’t need to speak to Durant to report on Durant, and Durant doesn’t necessarily know which of his friends and family talks to Smith.
But Smith is dead wrong about Durant ending this by signing a contract extension. The largest extension Durant could sign is three years, $69,887,423 ($23,295,808 per season). If he waits until the offseason to re-sign, his max contract projects to be five years, $144,536,025 ( $28,907,205 per season). I don’t know whether Durant wants to stay in Oklahoma, but even if he does, an extension is not a real consideration.