What is the peculiarity of document parsing by web driver?

Question

PHP

I am using Selenium and facebook/php-webdriver.
Team

$messages = $driver->findElement(WebDriverBy::id("messenger"))->findElement(WebDriverBy::className("messenger-channels"))->findElements(WebDriverBy::className("messenger-channel"));

returns the elements I need, and the command

$messages = $driver->findElements(WebDriverBy::className("messenger-channel"));

does not return. The difference is that in the first case, the necessary elements are requested through the parent, and in the second directly. What is the peculiarity of web driver`a and why the second command does not work?