Employee has had years to figure out how people communicate with them.
Maybe your employee does have more difficulty understanding than the average person, but this is such a bullshit excuse.
Everyone communicates differently. What is obvious to someone may not be obvious to others. Some people need a little more precision in the instructions you give to them. I don't see why it would be unreasonable to provide that.
I'm reminded of an interaction with my supervisor the other day...
Me: Hello. This case has <issue>. Am I ok to proceed with <issue> or does it need to be corrected first?
Supervisor: Have <Company name> figure it out.
<Company name> has literally thousands of employees so I have no idea why she said it like that.
Me: Uhh...do you want me to ask <Name of specific higher up person>?
Supervisor: No, have them figure it out.
Me: Who is them?
Supervisor: <Lower level assistant>.
For context, <Lower level assistant> usually asks us if they are ok to proceed, not the other way around.
Me: I don't think they will know the answer. Who should I have them ask?
Supervisor: <Company name>
Me: ?????
Supervisor: Have them ask <Name of a specific manager>
Me: Ok.
In this whole interaction, she was getting increasingly rude and irate with me for not being able to read her mind. If she would have just said she wanted <Name of a specific manager> to figure it out, she could have just told me to begin with instead of getting huffy and curt with me and unnecessarily prolonging the interaction.
Here's another example...
Supervisor: Hey, do you want me to move X out of the way somewhere?
Me: Nah, I don't mind it being there!
Supervisor: I don't want X there.
Me: <Supervisor>, I am not a mind reader. If you want something, you have to tell me.
Sometimes what is obvious in your brain is not obvious to those around you.