TL;DR All replacements for fopen() grow until they span multiple files.
The (default) on-disk database image is a single disk file with a well-documented and stable file format, making the SQLite4 library suitable for use as an application file format.
http://www.sqlite.org/pragma.html#pragma_journal_mode
WAL mode is a different beast specifically not intended to be a replacement for application format database, and it's not used by default.
So, no, SQLite is a single-file database. It provides more options than that, but the statement is true.
TextEdit in OS X also creates a temporary file when it saves a document, and then atomically renames it to the original filename; would you claim that RTF document consists of two files in this case?
More accurate would be changes being done by modifying blocks of the original file as well as appends on the end so that it is not valid by itself, and storing enough information to make it valid/undo in a second file.