Hey Mark,
that’s indeed a bug – one CSS declaration is missing; we’ve prepared a fix, please download and unzip this archive, and upload the resulting .css file into the /wp-content/themes/Origami/ folder inside your WordPress installation, using an FTP client or your hosting provider’s file manager. After doing that and refreshing the page the images should become proper size, please let me know how it goes.
Sincerely,
Andrii / Satori Studio