These icons are provided by Page builder and Shortcode, you could find them in Icon Box / Text List module and Icon / Text List shortcode.
All icons are set as icon fonts, they can be shown in high-resolution screen perfectly.
Using a iconfont instead of small images makes the theme faster (fewer requests to handle), more flexible (eg: you can apply colors to your icons) and allows for a more beautiful experience on smartphones and tablets, since they are scalable.