How does Shopify determine a 404 page status code?

I was wondering, what does shopify use to determine if a page is 404 or not? I opened a 404 page but all the network responses returned status code 200 OK. Which got me thinking, does shopify use some sort of proprietary status code fetch? I need this info so that I can write a function that checks if the page is 404 but as it stands now I cannot implement this function since the site always returns code 200 OK. I would greatly appreciate any help with this issue.