I wonder if Americans don't have a mental image for measurement units so that they alway use some physical object as a reference. Sure, its useful to use a common object as a reference but I don't see that much often in other places.
Most people usually understand what it means something to be 20 meters, 5kg or 2 liters intuitively. Like, when I hear that something is 60m tall I intuitively think if it as 20 story apartment building and don't benefit from the extra info about how this is like 18 elephants stacked on each other.
What's the difference between 18 elephants stacked versus a building with 20 stories? They are just different analogies.
Yes I'm always a bit dumbfounded by this behavior as well. They always use weird stuff and I never have the intuition of the actual size, especially since the definition can vary depending on context.
In this case, what is actually considered to be a small dog? To me it would be something that is close to the size of a cat but since it's about 13kg, it can't be that small, so that's more like a medium dog (I'm not certain, but I have a feeling that if you lay out things statistically this is what you would end up with). On the other hand, 13kg is very easy to get, that's just 13 liters of water, and it's quite easy to make a mental image for both volume and weight "feeling" that way.
American units feel so impressive and random, it is the reason they always add those weird comparisons but often they make it even worse.
Which is strange, since one of their measurement units is literally based on a body part.
Americans do not do metric. Americans can’t even balance a checkbook. Hence the small dog reference for mental “clarity”. We’re dumb. Just look at the news…
It helps to understand that the only freedom Americans only cared for (and the only freedom they have left from the looks of it) is the freedom to choose standards of measurement and vocabulary. This will provide historical context: https://www.youtube.com/watch?v=JYqfVE-fykk (Washington's Dream - SNL)
I guess you're in the minority here. In Germany, everything Remotely large will be measured in football fields or "Saarlands".