Forbidden functions to submit to wp themes dir

As you know themes are scanned before they are uploaded to themes directory. My submission were not accepted for two functions file_get_contents & curl , which i used for downloading themes files (css,preview image) from Bootswatch.

I checked docs but couldnt find any info on it, is there any way around it or is downloading of remote files absolutely not allowed ? Is wp_remote_get allowed by any chance ?