The Israeli Ynet news site says the soldiers were in a community centre in a village
Giffey, 43, who was previously family minister in Chancellor Angela Merkel's national government, will take over from the SPD's Michael Mueller as mayor after he decided not to run again.
The SPD scored 21.4%, slightly down from the 21.6% they scored in 2016, while the Greens came in at 18.9%, up from 15.2% and the far-left Linke dropped to 14% from 15.5%.
The SPD looks set to continue their current coalition in city hall with the Greens and the Linke.
Giffey, once seen as a contender to lead the SPD on the national level, stepped down as minister in May after a scandal surrounding plagarism in her doctoral thesis.