That is incorrect. The forced evacuation from the territory was because of collaboration between Wellington and the Portuguese government. It wouldn't have been done without Wellington's plan of withdrawal as well as building the fortifications. And Wellington knew that there would not be enough food to feed the 300,000 or so evacuees, as the Royal Navy couldn't bring in enough even with US shipping and foodstuffs.
And it was Portuguese workers that built the lines.
Interestingly, Wellington's headquarters were not in Lisbon during the period.
The two books I have read on the specific subject of the Lines by Fletcher and Grehan don't pull any punches and Pelet's memoirs about the planned and executed devastation on the way to Lisbon because of the forced evacuations, including executions of those who refused to leave, is quite enlightening.