Glad you enjoyed the hike! I haven't been up to the Hawk Watch in a few years, but it's a neat area for sure.
I checked the mileage for this particular hike, and it is about 2.4-2.5 miles based on our accurate GIS-based track of the route. A straight-line measurement of the trails is about 2.4 miles, but an additional 0.1 mile can be added to account for elevation and fine trail wiggles that might not be captured by the track.
I'm not sure how you arrived at a mileage of 3.25 miles, but since you indicate you followed this hike exactly, my guess is the track mileage from your GPS unit or phone may have been too high. Often, GPS readings can be fairly reliable, but there can be times where they are not quite correct due to a variety of potential errors. A GPS distance can sometimes differ based on type of device, the collection interval on the device, or even within different apps in a smartphone device. Other errors can also creep in, such as poor GPS satellite configurations and GPS wandering if you are stationary for a while (such as if you were at the Hawk Watch for an extended period of time).