Adobe Stock standard licence images social media?

It's nonsense what you have read about unmodified images. And even if the image is not marked as editorial use only, an attribution may be necessary. Editorial use only assets are not part of the free collection, btw.

Whenever you use an image in an editorial like situation, like a blog, you need to attribute the asset. That is the rule. So it may well be necessary to attribute. Nobody can tell you from the information you did provide if an attribution is necessary. If in doubt attribute, there is no harm done to attribute an image if it's not required. 

Look here for more information on licensing: https://community.adobe.com/t5/stock/links-for-licensing-terms/td-p/11366788
(Disclaimer: As always with licensing, this is my interpretation of the rules. I think they are correct and advice is based on reading and interpreting the licence terms and on fair use for both the buyer and the artist/stock company, but I cannot rule out that my interpretation is wrong. I'm not an Adobe employee).

You have to click through on the License Page to read the complete T&C's which includes much more info than what is shown on the summery page. Here's the section on Attributionn:

No, it is not necessary.