I can't imagine what would cause the image URL to be loaded in a new tab, because there is no code in the extension that can do what you have described when initiating a search. I'd be happy to debug the issue with you on GitHub, but please share some details about the browser, the search engine and the website or image you're using when you open an issue.

Are you by any chance using a screen reader or keyboard navigation and clicking the "Open image" menu item by mistake, instead of a search engine?

https://github.com/dessant/search-by-image/issues