Sometimes it is seen that when customers do a Global Text Search/Keyword search, it is returning some Kb's where keywords, for which you have searched are nowhere present on the article body. It might feel like the KB is returned randomly. However, it is not.
Release or Environment
The text search is returning results for the word(s) probably from the attachment present on the KB which is getting returned. By default, on kb_knowledge record, there is a dictionary attribute named "Attachment index", which makes the contents of the attachments to be indexed also for the KB they are attached too. Attachment of type .doc, .xls, .pdf, .txt might be containing the keyword in it, hence the data was returned.
By default, attachment indexing is enabled for the Knowledge Base. Enabling attachment indexing causes the platform to reindex the selected table, its parent table, and any children of the parent table. For large tables, such as the Task table, reindexing can take several hours and slows down the system until complete. Reindexing is best performed during non-peak times.
There is actually no issue in the behaviour and is an expected outcome.
The attachment indexing attribute only applies to the tables on which you explicitly add it. It does not cascade to child tables. For example, indexing attachments on the Task table does not index attachments on the Incident table. Not all file types are supported for attachment indexing. Please have a look at these below docs as well: