Often, the reviewer will not understand because he is not the intended audience. Other times, he will understand but he just doesn't like your method, because he is working in an opposite direction. Or maybe your method is a direct competitor of his and yours work better, which incentivizes some people to block your work.
Oh you mean those phantom "off topic"/"out of scope" reviews.
A good reviewer in this situation will review the referenced papers to bolster their understanding. A bad reviewer will expect everything to be spelled out within the manuscript, and, unfortunately, the length limits often don't permit that kind of write-up.