Yes we measure the end user experience. So if that is slowed down, and you meet the criteria for sending data, then yes those slow page loads will be included in CrUX.
In most cases, for sites popular enough to appear in CrUX hopefully the developers are but a very small sample of the overall page loads and not having a statistically significant impact on the overall CrUX numbers. Having DevTools open is often useful to debug what exactly is being sent to CrUX (
good guide on that here) so devs using that wouldn't want DevTools being open to exclude this.