A few weeks ago I received an email from the MSC that does church shops. It was an invitation to sign up for a new website for taking surveys. I thought the "invitation" was a bit tacky and unprofessional. Quite presumptive of them to assume that their database of mystery shoppers would be interested.
The situation you've described seems like it probably came from an independent scheduler who is trying to add to their "work from home" income. The scheduler used the opportunity to contact you so they could spread their personal affiliate links. I'd guess that the MSC does not endorse it. Either way, I view it as tacky and unprofessional. If this came from an independent scheduler, I think it's very sketchy.
Being registered Mystery Shoppers doesn't mean we (all) are interested in "get paid to click" for pennies or nickels. Or take surveys for a few quarters. Or sign up for cash back websites or use an app to earn points for gift cards.
I'll need to reread the terms that I've agreed to with MSC's. There might be a line in the agreement about sharing information with "affiliate" companies, etc... One MSC company claims to have over 200,000 registered users. I imagine the contact info/email addys of the registered users is quite valuable for marketing purposes.