Yes, there is a significant difference between a homogeneous mixture of hydrogen and oxygen in a 2:1 ratio and a sample of water vapor.
A homogeneous mixture of hydrogen and oxygen means that the gases are physically mixed together but not chemically combined. In this state, the gases retain their individual properties. This means that if you have a container with hydrogen and oxygen gases mixed in the correct ratio, you can still separate them, and they will behave according to their own characteristics. Hydrogen is a flammable gas, while oxygen is necessary for combustion, and together they can react under the right conditions to produce water.
On the other hand, water vapor is the gaseous state of water resulting from the evaporation of liquid water or boiling. When hydrogen and oxygen react chemically in that specific 2:1 ratio, they form water, which has entirely distinct properties from those of its constituent gases. Water vapor behaves differently from the individual gases; it is not flammable and supports life in ways that hydrogen and oxygen do not when separated.
In summary, the key difference lies in the state of matter and the chemical properties: a homogeneous mixture of hydrogen and oxygen is simply that, a mix of two gases, whereas water vapor is a product of a chemical reaction that formed a new substance—water.