Draw_tree mse vs. squared error

I noticed that the draw_tree method has different “error” calculations. mse has changed and wanted to know why in the lecture the same code gets mse, but when I ran the code template for 09_tabular it is calculating the standard error.

in lecture 7 draw_tree code output looked like this (i.e., mse=)

however, when I ran the code I got a standard error (see below)