Indeed, this is what you should do. Proceed a bit carefully if you don't have a good relationship yet with your manager: by good relationship, I mean knowing them enough to figure out how much you trust them.
You would also benefit from talking to other engineers who have more experience, especially in that company. It is easier to talk casually to people you don't report to.
It is difficult to give more concrete advice w/o more context:
* a "best case" scenario is that the senior manager (your manager's manager) was having a bad day, maybe got themselves into trouble for X reason. Managers are human too.
* another scenario is that your senior manager is actually still inexperienced. E.g. did not have time to talk to your manager first and then decided to skip directly, etc.
* a worst case scenario is that there is something weird going on between your manager and his manager.
[edit] A manager's manager talking to an individual contributor (you), especially about technical details of a project is just weird. It is hard for me to think of a scenario where I would do this. Why ? Because as a Manager's manager, you lack context about why certain things happen. And the person responsible for your outcome is by definition your manager. You mention both manager being smart people, "knowing their stuff": they may lack experience on the "people manager" side of things. That's often a drawback of working in very technical environments.
You would also benefit from talking to other engineers who have more experience, especially in that company. It is easier to talk casually to people you don't report to.
It is difficult to give more concrete advice w/o more context:
* a "best case" scenario is that the senior manager (your manager's manager) was having a bad day, maybe got themselves into trouble for X reason. Managers are human too.
* another scenario is that your senior manager is actually still inexperienced. E.g. did not have time to talk to your manager first and then decided to skip directly, etc.
* a worst case scenario is that there is something weird going on between your manager and his manager.
[edit] A manager's manager talking to an individual contributor (you), especially about technical details of a project is just weird. It is hard for me to think of a scenario where I would do this. Why ? Because as a Manager's manager, you lack context about why certain things happen. And the person responsible for your outcome is by definition your manager. You mention both manager being smart people, "knowing their stuff": they may lack experience on the "people manager" side of things. That's often a drawback of working in very technical environments.