There’s no reason to take this guy or his organization at face value when they make claims. It’s been hype and hopium for a decade now, fueled by TED Talks and wunderkind-loving media.
Cleaning up the garbage patch isn’t just a matter of collecting nicely floating big pieces of plastic. Doing that is good, but it’s not actually something that can ever get it to “clean”, it’s just something that helps slow the accumulation over time. You get the big stuff (relatively) easily, then it gets progressively harder, and eventually impossible.
Which is progress. It’s just not the lofty result they keep promising. If all it took was a big net and a relatively modest (by government standards) budget, this wouldn’t be a problem.
It’s a fine sample size. That’s a normal national poll. A poll of 1,000 people has a margin of error (from random sampling) of 3%. There are other errors than random chance that could bias a poll, but random chance is what sampling size is generally managing.