Yep. The error points to some of the website infrastructure component getting too slow. If don't know which webserver is used, but for sure, Mysql is the database server behind it. To ensure the site does not get blocked indefinitely, you have a timeout setting that make the website/php engine throws an error (and killing the sub-process) that waits too long for a response From Mysql.
The topic seems created correctly, and it involves multiple tables additions in database tables (at least, smf_topics, smf_messages), if the web server throws the error, it's because MySQL does not respond after the creation, or just after (to show the topic created, it has to launch a "SELECT..." request based on the topic id it just created). It may have appeared after a buggy update on one of the hosting components.
I don't know how to adjust settings, as I don't know the database size, the hosting infrastructure (a dedicated server with all the stuff on it, a shared hosting with web server separated from the database).
As long as the issue is not solved, isn't there a way to set a message on top when starting the new topic?
I bet it should be a good thing to calm down the rush.