I'm trying to understand in the context of the clinical trial, how a participant is using a "FHIR App" to populate a MedWatch Form 3500B? If you refer to the instructions on 3500B, it clearly indicates "Don't use this form to report: Investigational drugs or medical devices (those being studied) - report problems to your doctor or to the contact person listed in the clinical trial." 

Therefore, the Participant swimlane in the example is incorrect since we're talking about a clinical trial (i.e., not something that is post market). That means, the participant (do not use patient as that context means general clinical care) or clinical investigator reports/detects an AE. See instructions for 3500A below.

Lastly, the "Recorded AE" may be in an EHR or the site could be using a 1st (sponsor) or 3rd (CRO) party system to collect trial information. As such, this may seem to implementers that this is a formalized workflow and get confused. 

Reference: 

https://www.fda.gov/media/85598/download (3500B instructions)

https://www.fda.gov/media/133177/download (3500A instructions)