For what its worth, one of the entries on Dictonary.com defines a penthouse as "any specially designed apartment on an upper floor, especially the top floor, of a building." So, I guess they are playing within the rules.
Its just the very top floors its not exactly surprising they are marketing the three floors with significantly larger units as penthouses with one full floor penthouse unit at the very top. The plans on the website make it clear that the penthouse units are all much larger than the other units in the building.
How is it shady marketing. Out of the 100s of total units only about 18 are being marketed as penthouses and they have branded the full floor penthouse a grand penthouse to show that it is another step up. It is a little ridiculous and it is clearly more of a marketing scheme than anything else but it is not that shady. Not anymore so than claiming your building provides top of the line luxury finishes and the best service possible, which almost every luxury building does claim.
This looks great, hopefully this is an eye opener to the Nimby's that Boston can do height the right way.
NIMBY eyes are permanently closed.