It seems that there was good reason to challenge your numbers: you are using "concurrent users hitting my site" in a way that people in a website optimization context would not ever expect. This screenshot is talking about "concurrent visits", and has a figure for the average time that users were "engaged" (over 45 minutes). These are not performance measurements: they are the kinds of metrics you use to determine how interesting and sticky the content of your site is (along with things like your bounce rate and content flow).
In fact, this number (apparently a feature of Chartbeat) claims to be measuring "concurrent people sitting at a computer looking at pages from your site", not concurrent requests or "hits" to your webserver, or even concurrent HTTP connections (which may be idle for long periods of time). This number is almost entirely meaningless for the purposes of discussing your site's load. Imagine an HTML5 JavaScript game that took an entire day to play: with one request per second you may find yourself with tens of thousands of "concurrent visits".
In fact, this number (apparently a feature of Chartbeat) claims to be measuring "concurrent people sitting at a computer looking at pages from your site", not concurrent requests or "hits" to your webserver, or even concurrent HTTP connections (which may be idle for long periods of time). This number is almost entirely meaningless for the purposes of discussing your site's load. Imagine an HTML5 JavaScript game that took an entire day to play: with one request per second you may find yourself with tens of thousands of "concurrent visits".