My understanding of the physics is that SQUIDs only work at distances of max of 50-100mm, not more...

You seem generally very knowledgeable about this environment and I'm by no means an expert in the SQUID, but the way I understand it it's effectively a magnetometer with sensitivity down to about femtotesla scale. Clearly that could in principle pick up the magnetic effects of many objects well beyond a decimeter, even with consideration of the field rapidly declining with distance.

The main problem in using it, as I understand it, is rather that picking up everything the sensor could detect would usually result in an unmanageable deluge of unwanted information, and it's a normal operation context to filter the signal for distance so as to not pick up too much interference from equipment, staff, etc. But personally I don't see any reason it would be impossible to arrange it to band-pass instead of low-pass in that filtering.