I am just curious to know - which technology/framework was used to develop the Stack Exchange mobile apps?
Is it native Android and native iOS (Swift/Objective-C) or hybrid frameworks (React Native, etc.)?
I have experience developing iOS apps. Based on my technical interpretation, from extensively using both the iOS and Android clients, Stack Exchange mobile apps are developed using any one of the many cross platform mobile app development tool.
Speaking of iOS client, it lets you Handoff the current open post (on any of the SE site) to Safari running on a nearby Mac. This clearly indicates that the currently open view on iOS is running in within a Web view.
While the exact cross platform framework used could not be determined by this simple observation, but certainly the apps have not been developed using native development tools.
Another giveaway is the starkly similar interface across both iOS and Android clients, which is possible only when using a cross platform app development environment.