whilst I agree with your sentiment about not breaking laws etc. that line from the landowner about "wild habitat area" sounds like a load of horse manure.
next think they will be saying is that it was full of crested newts, barn owls or bats etc.
No, it's quite common to give access to a woodland area for walking. It's often encouraged by the local countryside rangers for specific natural events. Bluebells in full bloom kind of thing, easter egg hunts, badger watches and the like. Many estates plant up areas of native flora as reservoirs/hold outs of the old Caledonian forests. Many are on land that is too gnarly to ever have been much used anyway.
Locally the gills (steep sided burn gorges) are being encouraged as set asides just like those.
We already have the right of responsible access, but this set up really does look like it's extracting the urine on that and concerned the landowner enough that the police have been contacted about damage.
We also have laws about using airguns on someone else's land without permission, or using them where public access allows folks to walk .distance to footpaths and the like. Airguns need to be licenced here.
We'll what we see, but I think this looks like adults building a campsite on someone else's land without a thought about anyone else having access, or about the damage they were doing.
M