The Apartheid museum in Johannesburg notes that the sole act of violence committed by the ANC against civilians was a car bombing in Pretoria (1983). My South African colleague disputed this heavily. What was the level of the violence perpetrated by the ANC during the Apartheid years?

They are demonstrably incorrect.

uMkhonto we Sizwe was the armed wing of the ANC (commonly known an MK). My understanding is that the ANC has attempted to distance itself from certain aspects of their campaign of violence but the same key figures are involved throughout and all under the MK banner.

Just reading the "Truth and Reconciliation Commission of South Africa Report", one can find many other examples of violence against civillians, even cited by the ANC members themselves.

From late 1985 to mid-1987, some MK units were tasked with laying anti-tank mines in the rural areas of the northern and eastern Transvaal, targeting military patrols. A number of civilians – both white farmers, their families, and black farm labourers – were killed when these explosives were detonated. The ANC estimates that thirty landmine explosions took place in this period, resulting in some twenty-three deaths, including those of two MK members killed in the course of laying a mine

TRC Vol 2 p333

Alongside the Church St (Praetoria) bombing, there are individual accounts of bombings at Amanzimtoti, Durban Beach, Johannesburg Magistrates Court and several so called "soft targets". The justification for these was often that they were popular with either military, police or government workers. For example the Wimpy Bar at the Benoni Plaza was targeted (killing 1 and injuring 60) in 1988 because it was a popular spot for police officers to gather .

The reason some of these acts to not be included is that during the TRC, perpetrators could come forward and plead the case for amnesty. If they were found to be acting under the direction of the ANC then amnesty was generally granted. In the case of the Wimpy Bar, the perpetrators Tebogo Kebotlhale, Molwedi Mokoena, Phumzile Sigasa and Elgas Mabore Ndhlovu came forward and took responsibility for not only that bombing but the taxi ambush outside the Lindela Hostel in Katlehong. They declared themselves to be ANC members and were granted amnesty.

On the other end the Amanzimtoti bombing was viewed as against ANC policy, the TRC found that

Zondo was reacting in anger to the December 1985 Maseru Raid by the South African Defence Force (SADF). He was aware that civilians would be killed and deliberately acted against MK policy. In its first submission to the Commission, the ANC said that Zondo’s act was not in line with ANC policy, but was under- standable as a response to the SADF raid into Lesotho.

It is hard to really understand from an objective viewpoint how ANC could claim responsibility for only one act of civilian violence. I would imagine it will boil down to the point given above, essentially if the targets were civilian then it would be viewed as civilian violence. However if the targets were government, police or military, yet happened to have collateral damage then it doesn't count.