Way too few facts to judge yet.
Unfortunately, "if" it was a jolly, not being the future king they may not get away with the same perks!
Bit of a different kettle of fish with a chinook mind, that must be one hell of a garden! Hardly likely to have gone unnoticed either unless it was seriously in the middle of nowhere, the things are massive and incredibly noisy and tend to stick out a bit, especially with the tandem rotor.
We get chinooks landing in the park next to me to drop military and medical things off, we've had Sea Kings too. Not likely to go unnoticed, especially at landing altitude.
I'm sure I remember being told once how much it costs to keep a military aircraft like that in the air, was a scary amount and that was probably some time ago back in my RAF cadet days so probably higher now.