While somewhat stilted,an explanation is given in the prior paragraph. Basic idea is that the SETI pin sources a current 1/25,000th that of that flowing into the IN pin on the device, and whatever voltage that makes depends on how much resistance one puts in the way.
Yes: “linear” here is in contrast to “switching”, and refers to burning off an excess input as heat to obtain a desired output, while a switching scheme involves switching the input on & off to obtain a time-averaged result equal to the desired output.
Using the 29°C/W thermal resistance figure given, with a 5.5A current limit setting the part’s only good for about 800mV worth of voltage fold back (at room temperature) before the thermal protections kick in.
The preponderance of bench supplies these days are switch mode devices. The few linear models that remain can usually be recognized by their massive heatsinks or the burn hazards they pose for lack of such.