If an ASIN appears in a Search Term Report, then it most likely means a customer viewed a product detail page and your product appeared as a Suggested Sponsored Product.
There are also rare cases when an ASIN appears in a Search Term Report after appearing on a search page where that ASIN also appeared.
See the image below as an example.
And no, no one actually typed an ASIN into Amazon's search box. Most customers don't even know what an ASIN is.