Some QA people are members of the core QA team, and others are part of feature or platform teams. All are part of the QA Guild.
If you'd like to learn more, you are welcome to join the Mattermost community and engage with QA and others in channels such as these:
QA: Quality Assurance for general information and questions
QA: Weekly Meetings and the associated Board for info about our weekly Guild meetings
QA: UI Test Automation for info and discussions about test automation
QA: Contributors for info and discussions about contributing to QA efforts at Mattermost