I would think that's because market sizes are estimated based on...

I would think that's because market sizes are estimated based on a combination of factors like the number of people affected by the condition/requiring the product, what those regions generally spend on similar products, access to healthcare etc.
It's not a simple "this is how many people are in each market region and this is how much we sell the product for, therefore this is our global market size". In most market sizes I've seen for healthcare related products, the US tends to represent the biggest chunk.

In the US there's easier access to dentists, the procedure that Striate is used in is probably practiced more in the US than in some other countries with larger populations, and the US has a much higher healthcare spend per capita compared to the rest of the world (google countries by total health expenditure per capita, US comfortably sitting at the top).

Definitely still take it with a grain of salt, but I personally wouldn't think it's silly to see the US market representing 50% of this product's global market size. Sorry for the somewhat off-topic convo!