Summary: Sometimes the GSA will provide a suggestion for an alternate search term, preceded by the text "Did you mean." Occasionally, the suggestion has strange results or has incorrect spelling.
Cause: The GSA has a basic default spelling database. In addition, it will learn words from the corpus of documents it crawls, and add those words to its spelling database. If these words are spelled incorrectly often enough, the GSA will think that an incorrectly spelled word is correctly spelled.
Fix: If words are misspelled in your documents, correct those documents and then wait for the GSA to recrawl those documents. You can also force a recrawl on specific documents in the Admin Console under Index > Diagnostics > Index Diagnostics.
Additional Information: How Does the Search Appliance Make Spelling Suggestions?