No, telling him you are disappointed and hurt isn’t a grey rock, it’s opposite of it. Ignoring it and not replying to such texts at all is. Then later you could write (only if you have to convey something like if there is a specific info to convey) with “your stuff have to be moved out by 31st” or “appointment with our lawyers is scheduled for tomorrow” is a grey rock. End of communication. No engaging with emotions. Every time you show emotions it’s not grey rock and it starts cycle again. Grey rock method is meant to keep you out of a cycle and also hopefully to get other person to back off. He writes these things because you respond

When you react to him, you negate all your efforts and starts all over. I get it though. It’s hard not to react