Why do Product snippets appear when the “Enable Schema.org Markup“ option is ON, at the Google reviews widget?
Hi there, @Vasilis_Iliakis and welcome to the Community 
The thing is that our Reviews widgets use Product markup:
You can find more info in this article - SEO and Schema Markup in Elfsight Widgets - Elfsight Help Center.
If any questions come up, we’re always here to help 