This is consistent with the D&D 5E SRD, which clarified: Tremorsense can’t be used to detect flying or incorporeal creatures.
An incorporeal creature "has no body." In essence, it has nothing that would cause a vibration in the ground or otherwise create the movement necessary for an ability that by its very name senses "tremors" (aka a slight earthquake). Its ability to pass through solid objects does not make it cease to be incorporeal. With a rule saying otherwise, it's always incorporeal and can't be detected by a sense designed to detect earth movement.