Hmmm, I've been seeing this for a while now. I thought everyone knew about it. I've performed some searches where "only" the synonyms were in the top few spots and then came titles with the word I searched.
I'm diggin it! Why? Because I've been constructing titles for years that use synonyms judiciously.
Here's a great post from Bill Slawski that might shed some light on the matter...
More Ways a Search Engine Might Identify Synonyms to Expand Queries With
More information from Google...
Helping Computers Understand Language