The Meraglim say:
וְשָׁ֣ם רָאִ֗ינוּ אֶת־הַנְּפִילִ֛ים בְּנֵ֥י עֲנָ֖ק מִן־הַנְּפִלִ֑ים וַנְּהִ֤י בְעֵינֵ֙ינוּ֙ כַּֽחֲגָבִ֔ים וְכֵ֥ן הָיִ֖ינוּ בְּעֵינֵיהֶֽם׃
we saw the Nephilim there—the Anakites are part of the Nephilim—and we looked like grasshoppers to ourselves, and so we must have looked to them.”
How did they know how they were viewed? Why was that such a bad sin?