spear or pilum?

[Robert Vermaat]

Vegetius mentioned the kontos as an infantry spear by referring to enemy infantry as ‘contati’, as well as the ‘contus’ being used as a throwing weapon in a siege (Veg. III.6, IV.17). So here the kontus, a two-handed cavalry thrusting weapon, already becomes an infantry weapon that can be thrown

.....something is wrong with your references here - Vegetius wrote in latin(not greek), and there are only three books ( so no book IV) but whatever the correct source/reference, there is again no problem provided we remember the 'kontos' is the preferred greek translation of pilum( or as Vegetius tells us, latterly called spiculum)...so the pilum/spiculum is thrown in a siege, and barbarian infantry may carry it.

Well, my references are quite OK here, I checked it.
Book IV is mostly on siege warfare and, all too bad, the English translations online fail to translate it. Nevertheless we have a good online version from the Latin Library..
Anyway, even though Vegetius wrote in Latin, it is the terminology he used:
Veg. III.6: Iam uero utrum peditibus an equitibus, utrum contatis an sagittariis amplius ualeant,
Veg. IV.17: In superioribus autem turris illius partibus contati et sagittarii collocantur, qui defensores urbis ex alto contis missibilibus saxisque prosternant.

And actually, the description of the two-handed Sarmatian cavalry spears with a similar word as the (one-handed) infantry spear may not cause confusion, but it’s typical for the terminology – just about any pole arm is called a hasta in this list, whether it’s a two-handed infantry spear, a two-handed cavalry spear, a longer or a shorter infantry spear. If that’s not confusing I don’t know what is.