I take "FAANG-type tenants" to mean "Companies that aspire to FAANG levels of prestige" in an implicitly negative way, as in companies that are chasing the visible adornments of very successful companies such as open offices, micro kitchens, interns trying and failing to stay upright on Hoverboards, etc, instead of the things that actually made those companies successful. FAANG offices all have a particular "look" and that look is currently very trendy.