Hello Ian,
The reason you are seeing this difference is that your coworker is most likely using Apple's CoreLocation framework to get GPS information. Apple will only report 5m accuracy through CoreLocation with external receivers. Collector is connecting to the receiver via the ExternalAccessory framework and parsing the raw NMEA data from it directly.
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Ian,
Here is the Accessory Framework doc: ExternalAccessory | Apple Developer Documentation
Here is the wiki page outlining the NMEA spec: NMEA 0183 - Wikipedia
I'm not sure what your coworker is trying to achieve, but we also have some utilties to launch Collector from your application (maybe you can defer your data collection to Collector): GitHub - Esri/collector-integration: Multi Language repository that contains documentation and sampl...