Twilio is the software Heydoc uses to allow you to have a video consultation with your patient.
Heydoc is not involved in this relationship, it simply provides you with the technology.
The connection is between yourself and your patient only.
Source: Twilio Support
If you follow this link you'll find technical information but it also gives a good overview on how it works in great detail, and the fact that it’s end to end and HIPAA compliant.