Can you give a link to that sensor ?
Is a magnet attached to the spring ? I assume it is, otherwise the hall sensors can't detect it.
If so, the magnet is far more stronger than the magnetism of the spring.
Is the spring metal ? perhaps it is plastic.
With a reed relay, the metal contacts could be magnetised. That could result into a failing relay. But a hall sensor itself can not be magnetised. The hall sensors (as on/off switches) are also not very sensitive, they need a magnet nearby to switch.
If you want to measure small magnetism, use a HMC5883L magnetometer (compass) as a metal detector. That is a total different order of detection level.