So weird. Literally cannot remember if I've ever bought something from Shopify.
Tesla uses Shopify to sell cars -- I'd bet that just a few relatively large companies are the cause of that huge revenue number. Doubly so if eBay only reports their actual cut of sales as revenue instead of the entire sale price.
Your point stands that Shopify's largest merchants make up a huge proportion of GMV, but it's not because of big ticket items like cars.