It depends on the persons technique and mobility, but no. Pull-ups with good form DONT cause lumbar flexion.
The squatting has the same. People usually have a depth where lumbar flexion occurs. It migth be in pararrel or even above it. There is no certain depth. It's about the persons ability to move and control, and his range of motion.
You can see when lumbar flexion occurs by filming your squat, or putting a dovel to your spine to mark neutral angles (It should touch your sacrum, upper back and the back of your head.) Or then do a quadruple/kneeling assesment. Take a wide quadruple stance and just lean back and see when your spine flexes. It's easier to watch than read, check this:http://www.youtube.com/watch?v=0ecdkXfxQUA