It was on his way back past them, clutching a large doughnut in a bag, that he caught a few words of what they were saying.
“The Potters, that’s right, that’s what I heard —”
“ — yes, their son, Harry —”
Mr. Dursley stopped dead. Fear flooded him. He looked back at the whisperers as if he wanted to say something to them, but thought better of it.
He dashed back across the road, hurried up to his office, snapped at his secretary not to disturb him, seized his telephone, and had almost finished dialing his home number when he changed his mind. He put the receiver back down and stroked his mustache, thinkin . . . no, he was being stupid. Potter wasn’t such an unusual name.
(Harry Potter and the Sorcerer's Stone)
There is continuous auxiliary + being + adjective structure. In the context, its meaning is, I guess, ‘act foolishly (temporarily)’. Does the structure really have the meaning?