Contact records who Saved the date

Well, first of all, you're gonna need more than just one Smart Campaign. I assume you're using a webhook-based SMS provider, which means you need (as discussed elsewhere) 2 campaigns:

1. A batch campaign to select the leads and then use the flow step Request Campaign to call SC 2.
2. A trigger campaign, triggering on Campaign is Requested, that uses the flow step Call Webhook to send the SMS

Now back to creating the Smart List, i.e. the Smart List for SC1.  If it's based on them clicking a link, that would be either filtering on Clicked Email or Clicked Link, depending on whether the link was right in an email or on an LP.  But be very, very careful (again, as discussed at length elsewhere on the Community) about taking any action based on Clicked Email, since automated mail scanners click emails and you've no guarantee there was a human interaction.