Is it safe to assume that there is a link to your Smashwords page inside your books? If not then I would be looking to correct that ... and given that they have what they need to find you again, if they're interested, then I'd probably choose to live with it.
Another option might be to discuss it with Smashwords - since I imagine it is also in Smashwords interest to ensure that people find even freely available material from their website. In particular see their Terms of Service
where they say:
3b. Infringement by Others Upon Authorís Work. If an Author or copyright holder learns that a third party is violating Authorís copyright or pirating or illegally distributing a Smashwords-published work, the Author shall inform Smashwords; however, it is the Authorís responsibility to seek relief from the offending parties. If that work is published on Smashwords, Smashwords will remove it per section 3a above.