Does the related work section need to be strictly about other's work only? I would like to clarify a writing style issue concerning separating related work from my own work: 

Does the related work section need to be strictly about other work only? Or may you also explicitly explain the relevance of the related work to the text at hand?

That is, should you avoid explaining why a given related paper is related to your work and just report on the paper itself, or is it okay to also explain, WHY that paper is relevant while you talk about it? For example

Related work

[...]
Someone et al. (2010) report that "X -> Y". Someoneelse (2011) however found evidence for "not X -> Y". It is not entirely obvious where this difference in findings results from. That is why I study "X" in regard to its influence on "Y" in more detail in this thesis.
[...]

A version of this statement would also find itself in the introduction and possible the abstract, but imagine there to be more surrounding explanation in the related work section.

Is that permissible writing style? Or is the That is why I study "X" in regard to its influence on "Y" in more detail in this thesis. part out-of-place in the related work section?
The objective of related works is to, well, show how other work is related to yours. It’s not only reasonable, but also expected that you say how other works are positioned with respect to yours. When I read the related work section I also want to understand exactly that “why” of relatedness. Doing so explicitly would really help your readers.