I'll start off by stating the obvious. This meme comes from 4 chan, which has a bad reputation for racist drivel. The meme concerns the Rhodesian Bush War, which is a topic that often attracts a certain type of commentary fetishizing the tactics and efficiency of the Rhodesian military and ignoring political or racial aspects of the war. The meme purports to tell "something I read" but doesn't actually provide a citation to back it up, and makes sweeping statements.

All of those factors raise red flags, and your skepticism is warranted.

The ZAPU armed wing Zimbabwe People's Revolutionary Army (ZIPRA) received extensive materiel support and training from the Soviet Union, with the notion that ZAPU would form a conventional army to take on the Rhodesian armed forces head-on. ZIPRA recieved so much training and weaponry that ZAPU leader Joshua Nkomo would later remark that^1

By the end of the war we had tank crews, and even complete flying staff and maintenance staff for a squadron of combat aircraft, who had passed out of Soviet training schools.

Also, ZIPRA had the support Kenneth Kaunda and Agostinho Neto, giving the ability to establish bases in Zambia and Angola to train soldiers and strike from over the border into Rhodesia.

ZAPU/ZIPRA's main revolutionary competitors, the ZANU armed wing Zimbabwe African National Liberation Army (ZANLA), pursued a different military strategy of guerrilla warfare, mobilizing the Shona majority population behind their movement.

ZANLA also had different backers. ZANLA was given support and training bases in Tanzania and in Mozambiqe (the latter allowing ZANLA forces to strike into Rhodesia). ZANLA fighters also received training (both military and ideological) by Chinese army cadres in these Tanzanian and Mozambican bases.^2

Now, the amount of training varied due to the vagaries of war. When ZANLA was under pressure to mount a large offensive, in order to demonstrate their military relevance in comparison to ZIPRA, the large numbers of men to be trained would necessarily shorten the individual training. In that scenario, it is plausible that some ZANLA fighters would have gone into battle with limited time on the firing range.

But, I hasten to mention that this meme's conclusion that

none of them knew what a sight was for, they think that choosing the higher number makes the gun shoot harder.

is highly implausible, and I read it as racist hogwash.

In fact, for all of the faults of the Rhodesian regime in the 1960s and 1970s, it did strive to provide a decent standard of education for black subjects. To quote William Reno^3:

By 1959 Rhodesia’s segregated education system served 80 percent of seven- to fifteen-year-old African children, very high by African standards of that time. Primary and secondary schools were operated mainly by religious missions, although the state provided limited funding (about the same amount as provided for white pupils, who were one-sixteenth as numerous). In that same year, the country had twenty-four African secondary schools organized on the internationally recognized British Cambridge system. This differed radically from South Africa, where “Bantu education” was designed to produce unskilled and semi-skilled laborers, and gave Rhodesia’s early rebels a state-provided venue for ideological discussion that strengthened the roles of political commissars and cadres. Again, the bureaucratically effective state unintentionally provided the social spaces for centrally organized rebels to organize and challenge its authority over the population.

...

The economies of both Rhodesia and South Africa failed to absorb the school graduates produced by their relatively capable educational systems. In 1971 about 80 percent of junior secondary certificate hold- ers in Rhodesia remained unemployed six months after graduation. As a result a steady stream of politicized and otherwise unemployed students joined the guerrilla ranks. In the late 1970s the disruption of the education system in Rhodesia caused by rebel occupation of parts of the country forced the government to abandon schools that had served another quarter million students, some of whom then joined the liberation struggle.

...

Education systems in the white minority–ruled states generated more politically involved cadres and fighters, compared to earlier anti-colonial struggles. International agencies contributed to the education of majority rule rebel fighters to a greater degree than they had to anti-colonial movements. The UN High Commission for Refugees (UNHCR) helped coordinate the education of refugees, sponsoring schools that employed teachers supportive of the majority rule rebellions. In the late 1970s, the UNHCR helped to place 800 student refugees from frontline states in African universities. These services, along with food and health care, not only added to the reservoir of recruits; they also created social spaces where rebel fighters and cadres could develop expectations and political debates that strengthened the rebellion, while also posing challenges of control to the majority rule rebel leaderships.

All of these block quotes are meant to convey the sense that, contrary to the caricature in that 4chan meme, Zimbabwean revolutionaries usually had a high-school education and perhaps a university education for an officer or commissar. Entire cadres of ZIPRA or ZANLA fighters would not have thought "it makes the gun shoot harder!"

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1 Warfare in Independent Africa by William Reno, pp 92.

2 The Rhodesian War: A Military History by Robert Moorcraft and Peter McLaughlin, pp. 74

3 Warfare in Independent Africa pp 82-84