Detachable wings are a "feature" on most light aircraft.
Whether or not most of the rocket scientist pilots out there realise it or not I don't know, but most if not all wings on light aircraft are attached to the fuselage by some moderately sized aircraft AN bolts. Wing structures and attaching bolts / attachments are not designed for the force of hitting a tree, but rather are traingulated and engineered for those forces received during the flight, with margin of course.
Why do they do this? (detach wings at the root) Ease of buiding, parts can be assembled at different locations then shipped for final assembly, shipping of aircraft in containers, folding wings and maintenance etc.
Without knowing who the pilot was I'd suggest he might be a little old-school or Commercial given that he resorted to this measure. Last time I looked this procedure wasn't in the Bini's PPL syllabus.
I don't see what you are on about, it's by design, has happened many times before, will happen again and is probably a very safe option for crashing and when you have no options due to terrain!