They're just very small. If you look at the data, the risk ratios are in the range of 1.0x-2.0x, on outcomes which in healthy individuals are extremely rare to begin with. Same with the excess figures.
The logical conclusion given the rest of the data is that these outcomes would be concentrated in those who were very ill but below the threshold of hospitalization.
The study itself doesn't bin the groups far enough to show the implication for the asymptomatic or those with very minor symptoms, but there's a clear exponential trend that associates acute severity with long-term severity supra-linearly.