The phrase isn't that amazing is a common everyday expression of wonder, and as a short isolated clip it has circulated online as a reusable reaction sound. Short spoken lines like this spread through meme edits, compilations and social videos because they can be dropped onto almost any surprising moment without needing context. Its appeal is its sincerity in a feed full of sarcastic reactions, so it keeps being used for genuine wins, impressive skills and feel good reveals rather than jokes at someone else's expense.