Seems it might be looking at the referrer. Loading https://www.shopify.com/robots.txt https://www.shopify.com/robots.txt from clicking the link shows the weird

Seems it might be looking at the referrer. Loading https://www.shopify.com/robots.txt https://www.shopify.com/robots.txt from clicking the link shows the weird line while opening it in a private browser window shows the right one.