The PHP version requirement is clearly stated in the plugin’s short description and readme. Activating the plugin in a hosting environment without the minimum specified PHP version should result in the plugin’s deactivation and display of a dialog mentioning the incompatibility.
https://make.wordpress.org/plugins/2015/06/05/policy-on-php-versions/
Additional functionality may not be available based on the server configuration of the installing site. Twitter’s oEmbed API requires communication over HTTPS, a request which some servers are not capable of completing. Embedded Tweet and Embedded Tweet video functionality is disabled when WordPress HTTP APIs report the server is not capable of making a HTTPS request.
Previous versions ran on my CentOS distribution, but the current one doesn’t.
What Niall states is correct: the version requirement is clearly stated and the plug-in does not activate, and also alerts the administrator in the WP dashboard.
What Butch states is correct: not supporting earlier PHP versions is a cop-out.
Larger truth: the installed base matters.