>>9353648That's an assumption, a reasonable one but not necessarily correct. All the way back at the beginning Mega was using terms like "battle unit" and "combat unit" without strict definitions. Most of these "combat units" are indeed single-faction, but at least two are multiple-faction sets. The seemingly standard four-pack carded sets we got for years, the ones that always came with parts to build a display stand, were either all of one faction or two of each but their names followed the same pattern. The 4-pack that came with a Grunt and golden Hunter opposite a pair of ODSTs is labled "ODST Battle Unit"; one with a Brute Chieftain, active-camo Brute, Spartan Security and Marine is "Brute Battle Unit", to name a couple. Applying our own definition to something that Mega hasn't been consistent on is just setting oneself up for disappointment when they don't meet expectations.
As an aside regarding the set itself, "garrison" is an odd choice for the pack's name, given that there's no fortification or structure included for the Banished to garrison, nor is there an existing set to fulfill this role really. It wouldn't be the first time that Mega has provided for something that doesn't actually exist (looking at all you arctic UNSC pilot figs), still odd though.