On the thread number of shell version

[ech-o-o]

I am running Mobibench for a study of SQLite. After running the shell version with multiple threads, I found there are multiple databases created. In code line 1353, it saids:
"
sprintf(filename[db_i], "%s/test.db%d_%d", pathname, thread_num, db_i);
rc = sqlite3_open(filename[db_i], &db[db_i]);
"
while thread_num is the thread id running this line. As a freshman to SQLite, I wonder if this is a true multi-thread running way for SQLite in default mode (Not WAL but delete)? It looks like just running the program parallel instead of simultaneously access one database? Thanks for your kind reply.