Hi,
The credit card data is sent directly to Stripe with the Stripe javascript library over a HTTPS link from your browser to their servers.
If you look at the javascript included on the page, you'll see that the submit of the form is catched and the data is sent via a javascript AJAX call to Stripe. That's done by the Stripe javascript file. The submit of the form is there so that the Stripe library will use it to send to HikaShop the token generated by Stripe during that AJAX call.
If you want more details ; please contact Stripe directly.
Note however that since then, you have the let's encrypt website which offers free SSL certificates and Google now penalizes websites without them in it's results. So this question is moot. You should add a SSL certificate on your website. It's free, it helps for SEO, it reassures the users, and secures any data entered by the user on your website, not only the credit card.
Regards,