As NiceUnparticularMan mentioned, you really do have to control for industry. For example, your list included Bucknell, a college that has a business school and an engineering school. Both of those schools are known to generate high salaries and both are missing from Grinnell.
In addition, though, you also have to control for the past focus of the students that attended that school, as those past students are the ones whose mid-career income is being reported. To show you how much that can change over time, note that in 2014 the top career field chosen by that year’s Grinnell graduates who replied to the school’s post-graduation placement survey was “education/teaching K–12” at 13.8% of the respondents (https://www.grinnell.edu/sites/default/files/docs/2019-07/Class_of_2014_Report.pdf). For the class of 2022 that top spot had been taken by “Computing & technology” at 18.4% (https://www.grinnell.edu/sites/default/files/docs/2023-06/2022_FDS_report_draft_accessible.pdf).
If you are trying to guide someone in their quest for a college that would best fit them, the mid-career survey will likely not be of any help. There are just too many variables that impact the results and few of them will be relevant to your child.
Regardless of what your child wants to study, or even if they are undecided, I would suggest first sorting colleges that are best for that area of study, and then finding which best fit your child’s maturity, personality, future career and income goals. At that more granular level, not at the whole college/university level, the income and cost data become more relevant since they are closer in time, and career focus, to your child’s situation.
Good luck with your search!