Thats not a very good advice.

If you add lye and then shake the heat will rise way more rapidly. And if its hot and lye is left undissolved you shouldnt shake either.

Also rather stir then shake when dealing with lye.

If the lye is dissolved already shaking it does help mix it up because usually lye causes the the heat to be "trapped" at the bottom next to the dissolving lye. But please dont shake a solution with undissolved lye that is already near boiling. This will just end up dissolving more lye making more heat.

Threeyes yes this is way to hot. DMT starts to break down at near boiling temperatures so you want to keep the heat lower than 50°C at most times. But in your case it shouldnt have killed all the DMT.