It is more probable like $$\begin{align} \ce{NO2Br &-> NO2 + Br} \\ \ce{NO2Br + Br &-> NO2 + Br2} \\ \ce{2 Br &-> Br2} \\ \end{align}$$
The last reaction is a minor one in case concentration of $\ce{Br}$ is low.
The reaction rate order can be concentration dependent and need not be the integer.
In fact, it is rather mathematical parameter, related to solution of differential equations for a complex reaction system.
If the 2nd reaction is fast enough, the overall reaction rate is given by the slow rate of generation of $\ce{Br}$, which fast reacts to form $\ce{Br2}$
If the 2nd reaction is slow enough, it's rate $$k_{\rm 2}\cdot [\ce{NO2Br}][\ce{Br}]$$ can be written as $$k_{\rm 2a}\cdot [\ce{NO2Br}]^2$$
The exact solution is to solve system of differential equations for the rates of the concentration changes.
$$\frac{d[Br]}{dt}=k1.[NO2Br] - k2.[NO2Br][Br] - k3 [Br]^2$$$$\frac{\mathrm{d}[\ce{Br}]}{\mathrm{d}t}=k_1.[\ce{NO2Br}] - k_2.[\ce{NO2Br}][\ce{Br}] - k_3 [\ce{Br}]^2$$
For the dynamic equilibrium of the steady concentration of $\ce{Br}$:
$$\begin{align} 0&=-k1.[NO2Br] + k2.[NO2Br][Br] + k3 [Br]^2 \\ [Br]&=[ -k2.[NO2Br]+sqrt((k2.[NO2Br])^2+4.k3.k1.[NO2Br])]/(2.k3) \\ \frac{d[NO2Br]}{dt}&=-k1.[NO2Br] - k2.[NO2Br][Br]\\ \end{align}$$$$\begin{align} 0&=-k_1.[\ce{NO2Br}] + k_2.[\ce{NO2Br}][\ce{Br}] + k_3 [\ce{Br}]^2 \\ [\ce{Br}]&=[ -k_2.[\ce{NO2Br}]+\sqrt((k_2.[\ce{NO2Br}])^2+4.k_3.k_1.[\ce{NO2Br}])]/(2.k_3) \\ \frac{\mathrm{d}[\ce{NO2Br}]}{\mathrm{d}t}&=-k_1.[\ce{NO2Br}] - k_2.[\ce{NO2Br}][\ce{Br}]\\ \end{align}$$
