The cards are displayed for location searches where the intent is clearGoogle is working on a massive revamp to Google Maps. In the meantime, it's tweaking some of the smaller features as well.
Users are spotting a new way of advertising Street View content in Google Maps, with a card in the Maps OneBox for Google Search.
When searching for some locations, along with the map, you may also get a smaller thumbnail view of the actual location, as seen in Street View.
Street View content is already shown in Google search for some queries, particularly for businesses, but this addition should be a more helpful means of discovering Street View imagery, of which there is plenty.
The Street View image shows up in the Google Maps OneBox, the one inside the results column, not the Maps card to the side that shows up or some searches. Google displays the OneBox for searches that are obviously for a specific place.