There is no reason to believe random statements from characters in DBZ. They're the kings of hyperbole. If it wasn't shown then it doesn't count for anything.
Sorry but that's your take on it. Never seen Goku overestimate or underestimate any ki blast in the field (there's only examples of him correctly measuring the scope of ki blasts, like Buu's attack on earth), so when Goku and co. in the field sense the ki in any attack, I take it as fact and not hyperbole. And Yama is pretty high and wise-tier entity in DBZ.
You can stick to your opinion, but the fans aren't wrong in assuming 'X' blast would have blown up entity 'Y' if Z-Fighter 'A' hadn't stopped it. Afterall its the whole point of why A stepped in, and they can sense ki easily in blasts, unless otherwise stated.