Had a look on the internet, hard work finding good information on tendons behind the knee but found this:-
Hamstring Tendons: These are found at the back of the knee and connect the hamstring muscles to the bones of the knee and lower leg. They include the semimembranosus, semitendinosus, and biceps femoris tendons. The hamstring tendons and muscles are responsible for bending (flexing) the knee and extending the hip.
Also the tendon can come away from the bone. Did not find anything on snapping a tendon. I read how you did it in your other thread and that is definitely one way to damage the tendons, it was listed. If one of the tendon has come away from the bone:-
Because they contain no blood vessels, tendons heal slowly after being injured in any way. Non-surgical treatment of muscles pulling from the bone includes rest, ice, compression and elevation (known as RICE). However, in cases of severe injury, surgery is required to re-attach the tendon.
Get your knee checked out as others have said.
Hope this helps mate.