The authors report:
At baseline 1,775 (64.4%) men reported any coital injury including 1,313 (47.6%) soreness, 1,328 (48.2%) scratches, abrasions or cuts and 461 (16.7%) bleeding. On multivariable analysis coital injury risk was lower for circumcised than for uncircumcised men with soreness (OR 0.71, 95% CI 0.64-0.80), scratches/abrasions/cuts (OR 0.52, 95% CI 0.46-0.59), bleeding (OR 0.62, 95% CI 0.51-0.75) and any coital injury (OR 0.61, 95% CI 0.54-0.68).
So, these injuries — while minor — are fairly common and disproportionately affect uncircumcised males.
The authors suggest that this may affect the risk of HIV acquisition. This seems perfectly plausible, though it would be a mistake, I believe, to say that it is "the" mechanism by which circumcision protects against HIV. What's becoming clear, I think, is that circumcision protects against HIV through multiple mechansisms acting simultaneously.
I wonder, though, whether these findings might partly explain the fact that several studies have found that dyspareunia (painful intercourse) is more common among uncircumcised males?