I can't test on Elgg 1.x anymore but I've just tested on Elgg 2.3 and I think it should be the same on Elgg 1.8. Elgg searches only the title and description fields by default. I could verify this behaviour, i.e. a search term used in the title or description of an event resulted in this event shown as a result of a search. But searching for a term used for example in the long description of an event did not resulted in this event being shown in a search result.

For Elgg including other fields of an Event Calendar entry in a search it would be necessary to add a custom search hook to the plugin. I could add such a hook in a new release of Event Calendar (and quite likely will do when working on a Elgg 3 release hopefully soon) but I'm afraid I will no longer work on any new releases of the Event Calendar plugin for Elgg 1.x.