could be lots of causes - most of them minor especially since it dumped at the right rear. First, find out the last 2 digits on the coolant cap... it most likely s/b blue and end in .01 or higher (current version is .03). The .00 caps are notoriously known for loosing seal and causing the Boxster to relieve itself

.
If cap is .01 or higher, have a pressure test and or dye test done on the cooling system (obviously they should pay for it).
Let us know what you find out and if they refuse pressure test, then yes I'd pass as problem could then be relief valve, cracked tank, water pump or a # of things that will cost $500+ to R&R
Good luck
PS- Where in OH are you located?