The code is pretty self-explanatory.

If you’re interested in looking further:

Kobo’s current privacy policy says it collects reading-related usage information, including how often and for how long you consume digital content, as well as the genres, authors, and subjects you read.

Kobo’s Terms of Use contain a particularly relevant event explicitly called “Sideload,” which is described as occurring “when a user sideloads an EPUB.” So Kobo’s software does have telemetry associated with the act of sideloading.