In order to find a reasonable explanation, a few thoughts. Prior to the development of a guided missile, for example, regular aircraft are sometimes used to test components, guidance and so on. The Enzian was based on the Me-163 design. It was controlled by a joystick from the ground. This does not rule out additional help from ground radar as well.
Along with radar guidance, the fiery exhaust would be visible at night. After reaching a certain altitude, control could be passed off to an onboard guidance system. I have the names "Madrid" and "Elsass." The first relied on scanning infrared and the latter was a proximity fuse.
Sometimes the term "magnetic" appears when mentioning fuse types. The Fw-190 F-8 had a weapon called a Foerstersonde (SG 113 A) installed that fired rockets vertically, triggered by the magnetic field generated by a large metallic object, in this case, a tank. It worked on a similar principle to the handheld mine detector. A bomber is also a large metallic object.
Back to rockets. The Americans were seeing them as well. On 5 December 1944, the New York Times published an article titled "Rockets In Reich Defense." Here is the link to the NYT paid article site:
http://select.nytimes.com/gst/abstra...89D95F408485F9
An excerpt:
LONDON, Dec. 4 (AP) -- The Nazis shot "baby V-2's" or anti-aircraft rockets at formations of American Flying Fortresses that attacked Mainz, one of the German rail cities pounded by the Allied air fleets today.
"We got a lot more rockets than we usually do," said Lieut. Robert Dams of Milwaukee, a bombardier.
"The flak was light, but the Nazis mingled it with rockets which left heavy trails of bluish white smoke," related Lieut. David Barnett of Bromley, Ky., a navigator.
Ed