The base survey also pulled their data from less than 2000 individuals surveyed ages 18-73. Assuming that the distribution of ages was relatively consistent, that means by their definition of "millenial" (age 24-41), the data represents the responses of about 600+ people total.
BoA sponsored this survey, you always have to consider the source with stuff like this. They have a vested interest in getting people to use financial/retirement planning services, and if people feel good about how they are managing their money, they're more likely to employ these services. I downloaded the actual report, this sentence was in the summary right at the beginning:
"At the same time, we found that 27 percent are not saving at all. And more than three-quarters are weighed down by debt, with one in six millennials owing $50,000 or more, excluding home loans."
So according to their data, 3/4 of millennials are saving, AND 3/4 of them are simultaneously under large amounts of debt. I'm sure a significant portion of that is student loans. Almost 30% of millenials aren't saving at all according to their data, but it looks better for them to say 3/4 are saving.
Survey data can be spun in SO many ways, I would not take this info to be truly representative of the actual truth until I could see exactly what questions were asked, the economic demographic of the respondents, and the geographic data.
https://about.bankofamerica.com/assets/pdf/2020-bmh-millennial-report.pdf