In order to get the most economic benefit (for both the worker and the host nation) per worker, immigration limits, if they exist, should be based on a minimum income.

You are right that there is no reason to single out tech. However my claim is that this is because other professions have been successful in implementing the harmful protectionism I and the article were referring to. There is not a critical shortage of tech workers in particular, but high wages indicate a shortage in general. There are also valid reasons to focus on tech, e.g. tech skills are more transferable internationally than, for example, law.