All Zinc Chloride batteries (even the Tesco Value ones...) are relatively 'low magnetic signature' as the cell casing is Zinc (as opposed to the usual steel for Lithium / Alkaline primaries), and the active components are non ferromagnetic (unlike NiMh rechargeables). The total signature will depend on what they use for the top / bottom contacts. You can check them out with a little rare earth magnetic.
Is this brand particularly non magnetic?
Genuine 'Low magnetic signature' batteries are certainly available. They use them in science labs near Big Magnets for the opposite reason, so that the battery doesn't end up wrecking equipment at high speed! They may well be prohibitively expensive though.
Zinc Chloride cells have relatively low capacity, particularly with 'peaky' loads such as a disto.