If you have two utility functions $u(\cdot), \; v(\cdot)$ such that $v(x) = f(u(x))$ for some monotonic transformation $f(\cdot)$, then $u(\cdot)$ and $ v(\cdot)$ represent the same preference relation $\succsim$. This means that utility levels are meaningless to compare among individuals: if two individuals are such that one has a utility function $u(\cdot)$ and the other has $v(\cdot)$, they have the same preferences over their consumption space.
But when dealing with utility over monetary prizes, if you have two individuals with Bernoulli utilities $u_1(\cdot)$ and $u_2(\cdot)$ such that $u_1(x) = \varphi(u_2(x))$ for some concave monotonic transformation $\varphi (\cdot)$, then the individual with utility $u_1(\cdot)$ is more risk-averse than the one with $u_2(\cdot)$ (Mas-Colell Proposition 6.C.2).
My question is: how is it possible to conciliate the fact that both have the same preference relation $\succsim$ over the consumption space (since one's utility is just an monotonic transformation of the other's) and at the same time one is more risk-averse than the other?