I am definitely not OP. But I would guess there is some background agent or cron job running that populates his database from the dataset api. From that there is the web site that reads from the db to render the two visualizations - graph and table.
edit: on closer inspection it appears the charts are provided by squarespace. So maybe squarespace also provides the connector for back end data as well??
That's pretty much it, but charts are made with Plotly (R) and then hosted on AWS S3. We embed them in Squarespace code through Amazon Cloudfront to speed things up a bit. There area probably better ways to do this, but we don't know a ton about this so just used the tools we did know about.
His methodology page describes where this data comes from: https://www.govtrades.com/methodology
Incidentally someone sent me this link today; a list of charting libraries: https://thenextweb.com/dd/2015/06/12/20-best-javascript-char...
edit: on closer inspection it appears the charts are provided by squarespace. So maybe squarespace also provides the connector for back end data as well??
please correct me if I'm wrong or terse