Can the magnitude of DFT of a triangular wave be max for at 0?
What you see in the red graph is not an impulse ($\delta$) at zero frequency (in such case we would have a constant zero frequency which is equivalent to a constant dc signal $x[n]=c$).

What you see is actually a squared $\mathrm{sinc}$ function. You can easily verify that the frequency representation of a triangular function (both in continuous and discrete time) is in the form of $\mathrm{sinc}^2$. Look at here, for instance for the continuous triangular signal to see that

$$\mathcal{F}\{\mathrm{tri}(t)\}=\mathrm{sinc}^2(f)$$

and $\mathrm{sinc}$ has a maximum at zero.