What is adding zoom = 1.5 to embedded image?

I noticed a few posts on my blog have images that are stretched.

For example, https://www.portigal.com/blog/hertz-donut/

<img src="https://www.portigal.com/wp/wp-content/uploads/2012/03/hertz-form.jpg" alt="" title="hertz-form" width="425" height="749" class="alignnone size-full wp-image-17520" />

If I inspect the image, I see it’s URL is https://i1.wp.com/www.portigal.com/wp/wp-content/uploads/2012/03/hertz-form.jpg?zoom=1.5&resize=425%2C749

I gather the URL is Jetpack/Wordpress image caching. But what is with the zoom=1.5? Where did that come from? How can I get rid of it?

The adjacent blog post (https://www.portigal.com/blog/out-and-about-steve-at-sxsw/) is fine. My practice is to scale everything to 425 wide in Photoshop before uploading. Everything. But when I look at image properties, it gives me all sorts of different sizes. Is it this Jetpack thing that is scaling images up and down?

I’m fairly confused and apologize if this is a newbie question!