Definitely not a strict lockdown. We have had some lockdown, but there was no real restriction on movement or alcohol sales during the busy December period.
We had a super spreader event at the end of Nov/beginning of Dec - matric rage. Basically all teenagers finishing school (so age 18) go away and party for a week. Apparently several kids tested positive before the event and still went (well their parents let them go), and approximately 80-90% of people attending the event ended up testing positive. (more details on the event here:
https://www.iol.co.za/mercury/news/...-isolate-de502022-63fe-4d35-877e-ab3232504e21).
These teenagers then came home and spread it to their families etc. But now here is the kicker: mid-Dec to Jan is the busiest holiday period of the year, and the economy couldn't not have people on holiday. So all these infected people went on holiday, and the observed cases rate and recorded deaths absolutely spiked.
However, as you say, the number of cases and deaths are seriously underestimated given capacity constraints. In particular, this is shown by the number of excess deaths we have had over the last year vs. the average number of deaths from 2014-2019 (see the graphs on this site for a sense of how much underreporting is going on:
https://www.samrc.ac.za/reports/report-weekly-deaths-south-africa?bc=254). However, even the excess deaths are starting to fall dramatically. So, IMO, I think we have reached some level of herd immunity.