On iOS the post share uses the operating system’s share modal, and the topic share uses the Discourse modal. I’m not 100% sure the reason, but I think it is because the topic share has the invite button as well and we don’t want to lose that?
The JS error is unrelated, I’ll have a fix in soon (fixed in FIX: check is post exists (#2) · discourse/discourse-share-link-shortener@3d31c99 · GitHub).
How’s androids, windows etc? The main reason for my curiosity is I’m writing helps for my users 
Android and iOS should use the native share features when the share button is clicked on a post: Introducing the Web Share API | Web | Google Developers — desktop browser support for this is still weak, so it’s only a mobile feature.
Hi is there anyway to support the share icons to have the shortened url upon click?