Confusing regarding sub domains of main specializations EE?
The last line of the first complete paragraph of the snapshot says "Any main specialization can be combined with any secondary specialization." That seems to support what Dave Tweed said in his comment. Systems integration and optical communication are important aspects of many engineering specializations. "Smart City" likely refers to EE applied to the infrastructure of the modern urban environment. All of the main specializations listed would be applicable in that context.