How can I prevent my iOS app appstore page description from being indexed by search engines?
No, Apple controls the robots text for that website and publishes this information in the clear and allows search engines to crawl the App Store. 

Unless you somehow worked through developer support to change the terms of the license agreement and how Apple runs their web pages, you’re stuck doing a name transfer to a DBA (doing business as entity) or forming a proper corporation to own the app in Apple’s eyes and be published openly as the author of the app(s).