I don't think there's any way to use the data to determine if party switching is going on, but I wouldn't assume that's a major factor. Democrats aren't a monolith, and people who identify as Democrats hold diverse views on social issues. I'm not all that shocked by the drop. It's a bit less than half of the drop measured in Republican voters, and it probably demonstrates a general trend across the U.S., with more Republicans impacted than Democrats, which would make sense.