The part where he “gets to keep more of it.”

$1 in charitable contributions does not lower your tax burden by $1, and certainly not more than $1.

If that dollar would have been taxed as capital gains, assuming 20% capital gains and 3.8% NII tax, it saves 23.8 cents meaning the $1 donation costs 76.2 cents.

If that dollar would have been taxed as normal income, assuming a marginal tax rate of 37%, it saves 37 cents meaning the $1 donation costs 63 cents.

(These two examples are not intended to be an exhaustive list.)

Charitable contributions cost money, just not as much money as they would if there wasn’t a tax deduction.