The caption published in the book notes that Zug was one of the 'Sonderbund cantons', and implies that it might be surprising that the troops had assembled. The Sonderbund was a civil war in 1847-1848, which occurred because seven Catholic cantons (states) had formed an alliance amongst themselves against perceived threats to their religion from other sectors in Switzerland. The uprising was put down through the mobilisation of 100,000 Swiss troops, but not before 130 Swiss had been killed in several battles.
One of the legacies of the Sonderbund was the establishment of the 1848 Swiss Federal Constitution. For the first time, the Swiss became governed by a strong central government rather than being a loose grouping of cantons. This indicates how Switzerland in 1914 was not completely united and had its own problems which would not be helped by the stresses of wartime.