I'd read it as implying the opposite: that there are 40,000 moths out there who will wind up in a bear's stomach tonight. Like "some 40,000 people per day are hit by a car"; you wouldn't take that as meaning one car hit 40,000 people.
Sorry for being cheeky but the parent literally just addressed your question.
Neither figure seems particularly compelling here, of its "eaten by bears" it seems way too small if it's "eaten by a [single] bear" it seems too big.
"It is estimated that an ambitious bear may consume in excess of 10,000 moths per day, with some estimates ranging as high as 40,000 moths per day."
"One group of scientists analyzed bear scat and revealed that a foraging grizzly could gobble 40,000 moths in a day."