The two halves are screwed together with about 6 or 8 screws around the edge of the diaphragm.
If the pump you saw was a new one, I'm not surprised. Airtex fuel pumps are notorious for having all sorts of quality problems. I've had the valves pop out of position on at least two Cadillac pumps because they weren't staked in place. On two Airtex Ford pumps I've had the diaphragm tear within several months of operation.
