A technology platform is the foundation for building and running business applications. The platform allows users to run their applications smoothly without worrying about the technology that supports them. At the same time, it allows technical staff to rapidly extend, enhance, or upgrade application software, increasing the speed of business.
https://www.sap.com/canada/products/technology-platform/what-is-a-technology-platform.html
Pixelfed is definitely a platform . You only heard the term in context of centralized big social media so you think the term has bad connotation