The article says "Note that a transaction is using a DB-level lock that prevents concurrent writes—and sometimes reads—from the affected tables."

In innodb locks are row-level; myisam supports table-level locks though that's not and shouldn't be confused with a transaction; I don't know what a "database-level" lock is supposed to mean, are they really saying they're locking all tables to do a write? It doesn't sound like this author understands what a transaction is.