If the language shift was a learned skill that developed as part of performing the roles of the higher status, wouldn't two people of high status converse using similar rates, even if one of them is relatively higher than the other?
The article does not imply that this is a learned skill, since the whole theory is based on function words which are accessible at even the most basic proficiency of a language. It is merely describing what happens to our language when we enter a social interaction.
Note the words used aren't necessarily important but rather the function of the words are, i.e are they referencing social objects ( the role of pronouns) or referencing concrete or abstract non-social objects.
I'd suggest social status is always relative and is likely assumed by participants prior to their initiating an interaction: The student used lower status language when writing to the professor, who used lower status language when writing to the famous professor.
That isn't shown in the evidence, because the evidence in the article shows that the speech used is indeed relative.