isn't it somewhat unusual - following an accident - that the CAA takes actions that are not based on AAIB recommendations?
Not in the slightest is it unusual. It is absolutely normal for operating authorities to take whatever immediate action they need to eliminate or manage newly exposed risk.
If you want a high profile example, the Concorde fleet was grounded immediately after the Paris crash, and the accident board did not report for another 18 months. More recently think helicopters in the oil and gas sector.
There will be literally thousands of examples if you care to look.