They took samples from two locations; that doesn’t mean they were looking at only two data points.
The sediments get older as you get deeper down the core.
They also most likely did an “n” of three at least for every single data point in order to establish statistical significance.
Keeping a comparison simple is often the best way for an initial analysis; then do a mutli point comparison.
Johnny von Neumann used to say, “with four parameters I can fit an elephant, and with five I can make him wiggle his trunk.”
Yeah...if I took the data I’d explain it thusly. Regardless, very shallow sample location-wise....