Did you ask them if they get a lot of mice or rats going thru the hole for a better life. You didn't think of asking what that hole was for or why, so you are now guessing, and want us to guess along with you.
Their answer might be an easy fix, or no fix. When they add an addition with a crawl space in our row homes, they make a foundation wall hole to connect any heating, electric or plumbing to it. Sometimes its the only access to that under space.
There's a cross beam on the concrete wall, so no structural issue. And we need a foundation expert to guess the proper use of that small hole, or to throw some concrete in to fill it. How long has that addition been there without falling down, noting some catastrophic opinions here.
I'm glad i don't have some of yous doing appraisals on my own, fix and flips. However, if this is a sale and you are that nervous, you can ask for whatever calms you down. FHA and VA you might need to be sure. If you do ask for it, i would love to know the final results. However, we rarely get the final answers here.