Univariate Feature Selection

Link to the mission:

Without the dataquest guidance of plotting the three example features (Garage Area, Gr Liv Area, and Overall Cond), what would be the best workflow to choose the best single feature from the 20+ available?

What I did:

Using the data documentation, I made a list of all the numerical column names. I then made scatter plots of all of the numerical features plotted against the target (SalePrice) and calculated all of their correlation coefficients.

Overall Qual had the greatest correlation with 0.805, but this is a discrete variable. Of the continuous variables, Gr Liv Area had the greatest correlation with 0.699 (somehow different from the mission’s 0.709).

It makes intuitive sense to me to use a continuous variable for a model and therefore Gr Liv Area is the best choice based on the criteria of being continuous and having the highest correlation.

Why then did the instruction include a discrete variable in the 3 (randomly chosen?) example features? And what is the best way to approach this case of univariate feature selection outside the context of being guided?