Since there is a switch in Settings called Allow Siri While Locked, this is right up there with how Siri will sometimes say it can't give you Apple Maps directions while you're in a car.
The type of answer Apple promises Siri will be able to answer with Apple Intelligence.
In one case during AppleInsider testing, the problem was that Siri erroneously wanted to pass a personal information request on to ChatGPT, as if that functionality were in place and this was the correct thing to do.
Never mind that the beta of iOS 18.4 doesn't include the promised Siri improvements yet, Apple's voice assistant is now poorer than ever.
Sometimes asking Siri to "Delete all my alarms" will solely get you a text prompt asking if you're sure, but "what's 4 plus 3" gets both text and a spoken response.