This is down to difference in the classes output by different types of content in your theme’s search page.
The CSS of your theme restricts the width of Posts to 50% of the screen with this rule
.blog-area .type-post.size-2x1 {
width: 50%;
}
But for your project content, there is no ‘type-post’ or ‘size-2×1’ classes so the same constraint is not there. Images will be much wider.
I can’t tell you why these classes are coming out differently as thats something specific to your WordPress theme. It’s possible that to solve this properly you will need to change the code of the Search page template as well as adding some more CSS, specific to the needs of your search page.