Well, the many far left movements had a militarist element (directed against the bourgeois) to them from the very beginning.

They sure had a culture of violence, as in street fighting and insurgency etc, but under Stalin it turned into proper militarism, as in: approval of army hierarchy and officer-caste ethics as not merely necessary but laudable; formal expressions of loyalty turning organization-based rather than class-based; displaying the expected World Revolution (in films, lectures, etc) as being in essense a conventional war, with near-identical armies facing off and some aid from working-class sympathizers - rather then the preceding image of a massive popular rebellion... A somewhat-revisionist Russian historian, Mark Solonin, describes how the massive military build-up was accompanied by this gradual shift in propaganda from "revolutionary violence" to "Red militarism".

Also the nationalism didn't start going until WWII

Believe me, it did! It was crypto-nationalism in the 30s, but back then Stalinist propaganda already began to lionize the historical achievements and the "properly" anti-feudal, anti-bourgeois sentiment of the Russian Volk. It appropriated 19th century authors like Pushkin who were previously fashionable to reject as retrograde.
There's a sharp contrast between the 1920s' propaganda line on Imperial Russia (backward, miserable, completely lost but for the Communist guidance), the lambasting of "Russian chauvinism" as a right-wing deviation and the insistence that all Soviet nationalities should harmoniously melt into a purely political whole - and the 1930s' quiet suppression of all that, with Old Russia called less a benighted rural wilderness and more a supremely talented nation, naturally predisposed towards communism, that only needed to overthrow Tsarism to assume its rightful place of world leadership.
I've read a few Russian studies about the relationship between Stalinism, Soviet culture and propaganda; they offer a far more nuanced view than the one you cite.