composer-bin-plugin: Error during bin require with Symfony Flex

While adding a bin requirement I got an error like this:

$ composer -V
Composer version 1.6.4 2018-04-13 12:04:24
$ composer show | grep "bamarni/composer-bin-plugin" 
bamarni/composer-bin-plugin        v1.2.0            
$ composer bin phpmetrics require phpmetrics/phpmetrics
Changed current directory to vendor-bin/phpmetrics
Composer could not find a composer.json file in /Users/brzuchal/Workspace/data-dump/vendor-bin/phpmetrics
To initialize a project, please create a composer.json file as described in the https://getcomposer.org/ "Getting Started" section

Am I doing something wrong? Documentation doesn’t say anything I need to do except require composer plugin.