Issue with getting distributions/mailing lists

I'm fairly new to APIs, and I found something very odd. I'm running through a process to get all distributions/mailing lists for a set of surveys.
I have a test survey that I only sent to myself. But running through my loop, I'm seeing a distribution/mailing list set that was not used for this survey. That is, I get all distributions for a survey, then all mailing list contacts for those distributions. And the results show a set of contacts that were never sent this particular survey.
Has anyone seen this?

I'm using "$url = "{0}distributions?offset=0&surveyId={1}" -f $urlbase,$SurveyID" to get the distributions, and
$mlurl =  "{0}mailinglists/{1}/contacts" -f $urlbase,$MailingListID to get the contacts.
(this is powershell)