This was from 1847. The failure of the Vienna Uprising in October 1848 dashed their hopes and (further) radicalized Marx and Engels. Your progressive heroes lashed out at various socioeconomic or racial and ethnic minority groups for failing to support their cherished workers' revolution.
Enraged by what he perceived as the Viennese middle class's failure to form a united front with the revolutionaries, in November 1848 Marx wrote that "no peace with the bourgeoisie is possible, not even for the period of transition" and "there is only one way in which the murderous death agonies of the old society and the bloody birth throes of the new society can be shortened, simplified and concentrated, and that way is revolutionary terror." He would subsequently write in the Communist Manifesto that "The proletariat of each country must, of course, first of all settle matters with its own bourgeoisie...the violent overthrow of the bourgeoisie lays the foundation for the sway of the proletariat".
In January 1849, Engels blamed "counter-revolutionary" races and called for their genocide:
The Austrian Germans and Magyars will be set free and wreak a bloody revenge on the Slav barbarians. The general war which will then break out will smash this Slav Sonderbund and wipe out all these petty hidebound nations, down to their very names. The next world war will result in the disappearance from the face of the earth not only of reactionary classes and dynasties, but also of entire reactionary peoples. And that, too, is a step forward.
Once you're on board with eradicating "counter-revolutionary" classes and races, depriving them of arms is a mere formality. The "workers" in Marx and Engels refer to industrial workers who had attained class consciousness only, not the "lumpenproletariat" (workers who were deemed incapable of class consciousness), "petite bourgeoisie" (middle class), landlords, or peasants. Gun control advocates have never had a problem with their side having guns.
Lenin put Marx and Engels into practice, founding the world's first Communist state on a program that included gun control to better facilitate State violence:
One cannot hide the fact that dictatorship presupposes and implies a “condition”, one so disagreeable to renegades, of revolutionary violence of one class against another … the “fundamental feature” of the concept of dictatorship of the proletariat is revolutionary violence.”
Disarmament is the ideal of socialism. There will be no wars in socialist society; consequently, disarmament will be achieved But whoever expects that socialism will be achieved without a social revolution and the dictatorship of the proletariat is not a socialist. Dictatorship is state power based directly on violence.
We are not in favour of a bourgeois militia; we are in favour only of a proletarian militia. Therefore, “not a penny, not a man”, not only for a standing army, but even for a bourgeois militia, even in countries like the United States, or Switzerland, Norway, etc.
Our slogan must be: arming of the proletariat to defeat, expropriate and disarm the bourgeoisie. These are the only tactics possible for a revolutionary class
Only after the proletariat has disarmed the bourgeoisie will it be able, without betraying its world-historic mission, to consign all armaments to the scrap-heap. And the proletariat will undoubtedly do this, but only when this condition has been fulfilled, certainly not before.