Yes, searxng is indeed making requests to all configured search engines.
The intended use of searxng is to proxy searches for many users, making tracking individuals difficult for the search engines, since everyone's data is mixed together.
Using searxng does however also bring some benefits if used by one person only:
- no browser fingerprinting
- convenience: get results from across many search engines at once
I personally use a private instance mostly because I like the simple search results page.