The confusion comes from naming American units "imperial" - after British, and having international - metric - system created by the French revolution, with "liberte" an important goal. So it could be argued that it's actually SI which has freedom units. On the other hands, Americans are quite often characterized as freedom "distributors"...
Most Americans that I have pointed this out to look at me in disbelief. The vast majority have never heard of US Customary Units. Whenever they refer to their system of measure they say imperial, and many are unaware that volume measure in the Imperial system is different from US Customary. I fought again the use of imperial as the name for the system for over twenty years in a multinational company to no avail.
Send them this handbook from NIST! :) Section 2 covers all of the customary measurements, some with names hardly anyone knows (Apothecaries Units? Gunter's Chain Units?)
I've never met a Canadian who gave their height or weight in metric units.
Or a recipe in Canada that doesn't set a temperature Fahrenheit. Also: the size of TVs and screens. Or paper.
News articles in particular tend to go out of their way to use strange units of measurement. Bananas, fishes, football fields, car lengths, swimming pools... Anything but SI system of units. Even the feet gallon pound values are rare finds that need perseverance.
Eagle wingspans isn't something I've seen used, but the football fields unit does make sense when talking about something which is relatively long (can be measured in 1/2 to 3x the length of such a field).
If you tell the average (US) person 1000 feet, they won't be able to envision it. But if you say "a little more than three football fields", they can visualize that.
The point of strange units of measure is just to make a quantity relatable.
It's a commentary on all the unique and interesting ways Americans appear to measure things.
Sometimes people will take it further by, for example, converting a length in meters into football fields or bald eagle wingspans.