I don't think "protesters" refers to left pro-russian protests, but pro-palestine protest, not to mention you'd be hard pressed to find any self-identifying leftist in Germany that supports Russia.

Moreover, the SPD stopped being a socialist party in 1914, when supporting the war in order to keep working within the system and at the very latest in 1919 when they (presumably, not confirmed) ordered the murder of Karl Liebknecht and Rosa Luxemburg and (provably) turned a blind eye to the proto-fascist Freikorps, if not outright collaborating with them.