There appears to be a bug or a hidden feature where after sending a message in Messages and you hover over or touch near the back button in the top left, voice memo activates and starts recording. This is an unexpected behavior and it has been an issue going back several iOS releases to the current release. This has happened on various phone models, so it isn't limited to a specific model.
In addition, (and yes, this does add a second bug/issue) there is a hidden feature where touching in the top left of a message thread, above the back button, causes the focus of the message thread to jump back to some texts/messages from an earlier time. This is unexpected and seems like it should be addressed.