You should consider that this is obviously a "study" meant to manufacture data to support the organization's favored position not a real investigation into what actual people think.
Their conclusion is based on multiple surveys with different questions and methodologies but consider they did things like ask first, ": Before today, had you heard about a challenge called Plastic Free July, which encourages people to refuse and reduce single use plastics?" Told them about the harm single use plastics cause and then asked them, " How important or unimportant do you believe it is to have an
internationally binding treaty to combat plastic pollution?" To which a large percentage of people obviously responded that yes it is important.
In another survey they asked, "The United Nations agreed earlier this year to develop
a global treaty to end plastic pollution..." with the following question then referencing this treaty, "The treaty will include global rules for participating countries. How important or unimportant do you believe it is to have global rules to:" To which one of th responses was, "Ban unnecessary single-use plastics.", another was, "Ban types of plastic that cannot be easily recycled", etc.
And then they interpret agreeing that there should be a treaty to stop plastic pollution immediately after being given information about how bad it is to be the same as "Ban on Single-Use Plastics" which by and large no one surveyed actually said they wanted explicitly, nor were they asked.