Parallel Termination in a Transmission Line
But if the source impedance \$R_s\$ of the driver doesn't match with the
line impedance \$Z_o\$, shouldn't there be reflections still at the driver
output from the line?

Yes, there will be miniscule reflections between the driver output and the start of the transmission line. If that distance is greater than &quot;very short&quot; then the reflections will increase and could cause a problem. However, we try and ensure that the track distance between driver output and transmission line is short. This means that reflections are small and insignificant.
You can also get mismatches caused by the receiver input capacitance/impedance shunting the load resistor \$R\$.