I’m not sure why Shopify has changed this within the past year or so but before shopify counted a “reached checkout” when someone got onto the shipping method page at checkout which made things so much similar and easier to understand however now a days shopify counts a reached checkout as someone who just lands onto the checkout page - there’s no indication on what page the person left on and doesn’t create a ‘new customer’ within admin.
I find this very backwards not useful in my opinion if you are trying to understand your data on what can be improved.