This sentence would probably be a citation in APA style. Citations on research papers are very important since they give due credit to the original owner of the statement. Statements that don't have citations tells the readers that those statements are of the researcher/s alone which would be a problem for them if found out that it wasn't theirs to begin with. This would result to a work of plagiarism which is a grave sin in constructing research papers and is more equated with the act of stealing.
It is explanatory because the extension in the simile gives the audience with a more descriptive image of the thing that is being described.
Similes provides an image to the reader by <em>comparing </em>using the words "<em>like" </em>or <em>"as"</em>. When the simile is then extended, the initial image is given more meaning creating an explanatory effect on the audience.
