Wheel Rim problems of the 2005 Toyota Matrix

I have a 2005 Toyota Matrix xr with 16" alloy wheels. I hit a cobblestone sized rock in the rock with the left rear wheel at about 50 mph. The tire lost pressure because the alloy wheel split in half like a bagel sliced down the middle. Toyota would not fix this as a warranty item indicating there was no evidence of a manufacturing defect. However, none of the service personnel had ever seen a wheel split in half. I've contacted Toyota's customer experience center and reported the incident but they also indicate this is not a warranty issue and referred me to the dealer customer relations manager who gives the same explanation. I believe there may be a defect in these alloy wheels but have found no other reports of such damage on the NHTSA site. I want to make sure this incident is documented in case these wheels are found to be defective.