[Festro]

It's not a proxy search engine thing.

Bing (and Google) serve internal site search pages (your search function) in their search results if they're able to crawl your search function (it's easy to find, and as longas it's indexable).

What they don't really know is what terms people tend to search for on your site, as that's only known to you. So, they'll guess. And they'll guess terribly and in random languages.

I think Google are okay at making informed guesses now, but Bing as usual lags behind.

I wouldn't worry, this just means that your search results might appear in Bing's index and you may get traffic for terms your site hasn't been ranking for previously.