The comparison to higher education is apt. Prices at community colleges (and many universities) are set in dollars per credit hour. Credit hours, though, aren't the same as clock hours. I taught a three credit hour class that met three times weekly and lasted fifty minutes a session. The school, naturally, advertised this discrepancy well in advance of taking payment. (I do wonder whether there's any case law about that.)
It seems that office managers are setting prices in dollars per real-estate square foot, which is a different unit of measure from the commonly understood measure of area. Maybe they should advertise "real-estate square feet of office space" instead of "square feet of office space" to eliminate the confusion that comes from overloading that phrase?
(Whether this sort of linguistic imprecision and flux is a good idea is a separate argument, to be sure. This sort of shenanigans increases the burden-- and therefore the cost-- for people trying to purchase a good or service.)