Responsive image not working as expected

Hi,

On this article https://spoelstra.ws/licentie-uitleg-wordpress-themas-themeforest/ the first image is using responsive techniques:

<img class="size-large wp-image-1777" src="https://spoelstra.ws/media/regular-en-extended-licence-themeforest-620x304.jpg" alt="Regular en Extended Licence Themeforest" srcset="https://spoelstra.ws/media/regular-en-extended-licence-themeforest-300x147.jpg 300w, https://spoelstra.ws/media/regular-en-extended-licence-themeforest-620x304.jpg 620w, https://spoelstra.ws/media/regular-en-extended-licence-themeforest.jpg 1009w" sizes="(max-width: 620px) 100vw, 620px">

As you can see there is a 300w image available. When I make my browser screen as small as possible, it meets the given ‘max-width 620px’ media query where the image is 100% of the viewport width.

However, still the default 620w image is being used. What is going wrong?

Kind regards,

Willem