Temperature relates to how fast atoms are moving. If they're moving very fast, then we say it's very hot. Damage from high temperature however requires a substa

Temperature relates to how fast atoms are moving. If they're moving very fast, then we say it's very hot. Damage from high temperature however requires a substantial quantity of those atoms, not just that they be moving quickly. But there are very very few atoms in the interstellar medium. They are moving very fast, but there are very few of them indeed. To incinerate something, there would need to be a lot of atoms indeed moving at high temperature. An isolated atom hitting the probe, even at relatively high speed, won't be doing much incinerating. It's like a sparrow hitting a building. Won't do much, even it's a fast-moving sparrow. But a billion sparrows hitting it in unison - that might be a problem.