That's correct but most SSRs can be directly driven by the Arduino, as long as they are rated to be driven from 5V. The specs I found say 12mA for that relay and the Arduino can put-out up to 40mA (20mA max recommended).
That's not the case with most electo-mechanical relays... They usually need a driver circuit.
Some SSRs require an external current limiting resistor (not this one), and then they can operate from almost any voltage with the right resistor.
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