He definitely didn't think his status would change or that his security would be removed.
I think he'd asked for meetings about going part-time, was told No part-time wasn't happening but they could discuss at a meeting on x date and he kicked the toys out the pram doing a press release saying they were no longer going to be Working Royals.
I think he reacted before talking it through calmly with the family and getting proper legal advice.
Almost like he thought his Gran would bow down to him except I think by that point Charles and William were having more of a say in the running of the Monarchy.