After 15 years, the polling firm changed the way the question was asked: "Half of the respondents were asked about evolution in a two-step process much like the one described above. The other half of respondents were asked a single question about their views on evolution and given three response options" The graphic is pretty self-explanatory.
pew evolution poll
The pollster wanted to avoid forcing people to choose between science and religion:
The results of the new experiment indicate that there are some people who do believe that humans have evolved over time, but who, for whatever reason, did not say so in our traditional method of asking about the topic. Perhaps without the opportunity to immediately connect evolution to God, some religious respondents may be concerned that expressing belief in evolution places them uncomfortably on the secular side of a cultural divide. "The Evolution of Pew Research Center's Survey Questions About the Origins and Development of Life on Earth" at Pew Research Center
Darwinian evolutionary biologist Jerry Coyne (hat tip!) doesn't like what happened to Naturalism (nature is all there is), often called "materialism" in the numbers:
As you see, if you give people three alternatives at once, pure creationism falls from 31% to 18%, theistic (guided) evolution rises from 27% to 48%, and, surprisingly, unguided, natural evolution falls from 40% to 33%. Somehow Pew sees this as good news, though I don't: if you lump those who see God directing evolution (a watered down form of creationism, like Behe's) with de novo creationists, the total of non-"naturalists" under the new protocol is 66%, while it was 58% before. And there are 7% fewer people who accept naturalistic evolution under the new protocol. --Jerry Coyne, "Americans' acceptance of evolution: does it depend on how you ask them?" at Why Evolution Is True
Actually, it's not surprising at all. Pure naturalist atheists are not that common once you get off campus and a safe distance from the raging Woke. Most people would rather you think they were creationists (provided you don't push it too far), which likely accounts for the drop in the second set, when a clear alternative for theists is provided. Some of us think this change in questions is long overdue.

Other polls will ask different questions (they have to) and get different answers.