I created a new view based on search_api_solr with indexed title field and the filter of content type article.
I setup an entityref version of the search_api_solr based view.
While testing the preview, the view works just fine on indexed nodes.
All nodes are indexed.

I set the field in my content type to select list.
I selected it for the entityref selection widget for a field.
But when I use it as an entityref view, the view is not used to filter.
All content is returned. I would have assumed that the content would have been filter by at least the article type.
Instead all content is returned for all content types.

When I use a regular node based view with the title field (not indexed), entityref works just fine.