No, a total of 4 people 4 flights.
The boat was a zero emissions sail boat, has solar panels and underwater turbines that generate electricity onboard.
This from the fossil fuel industry who are heavily bias but on this point had to admit:
Greta’s showy sea voyage, while generating C02 through the flights of the very people who sailed her to New York, is having an effect in spurring people to abandon or at least reduce the number of miles they choose to travel by air. In the end, we suspect that the four flights generated by her trip to the US have been more than offset by shamed people who have since forgone flying. Some may still see this as an act of hypocrisy, but the resulting math still comes out ahead in favor of reduced C02 generation.
& this is their conclusion despite their many criticisms of her:
"While Greta’s carbon footprint isn’t as small as she’d like due to her extensive travels, her carbon footprint is likely smaller than most."
https://oilprice.com/The-Environment/Global-Warming/Greta-Thunbergs-Not-So-Little-Carbon-Footprint.html