Not correct in every case. Read the decree.
It does cover no tax on "remitted" income.
If WW tax comes into to play it will not all be tax free.
Example: income outside Thailand is
$10,000 a month. You remit $5,000 tax free. The other $5,000 would be taxed.
LTR visa does not cover all WW income unless all income made abroad is remitted.