بِمَا لَمْ تَسْمَعُوا أَنْتُمْ وَلَا آبَاؤُكُمْ points to unfamiliar claims. The report does not mean that all previously unknown information is necessarily false; rather, it warns about deceptive religious reports.
Example 1: If a message promises extraordinary religious rewards without giving a source, do not forward it automatically.
Example 2: When attribution is uncertain, do not present the statement as a confirmed saying of the Prophet ﷺ.
For a beginner, consulting a recognized collection and qualified teacher is a practical safeguard.