The reference to " other isolated outputs are all capable of driving the relay "

differentiates the outputs from the 5V logic level outputs that you connect to other logic gates or the stepper driver step & direction inputs

from the open drain outputs designed to switch inductive loads like the relays

As an example
Going back to equipment I used and maintained in the eighties
all the logic was built from 7400 series TTL logic

Typical gate inputs passed 1.6 mA when an input a input was grounded
and the outputs could sink 16 mA
so you could only connect 10 inputs to the output of an IC
unless you used a buffer that could pass more current

To connect to other devices like tally lights for the control panel switches

A lamp “driver” / BCD decoder like the 7445 switched 28v bulbs ( run off a 24V supply ) by grounding the other end of the bulbs filament

The 74141 being another version with high voltage outputs for driving Nixie tubes
(which is basically a neon with an anode connected to 180V DC via a resistor and 10 cathodes shaped in the form of the digits 0 to 9 that glows when grounded )

These days you would use a 7447 BCD to 7 segment decoder driver connected to a 7 segment LED display or LCD

John