Yes, this is done with Seaside web framework. We also use Bootstrap, Ajax almost everywhere, JQuery, etc. Obviously we also use several JS libs like Highcharts, Datatables, CodeMirror, TinyMCE, etc.

Pharo has it's own UI, but can also run native OS UI windows (this feature is being improved). What you are seeing in the screenshot is indeed a web interface and a Seaside application appears to be hosting it, according to the description