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It isn't, no. It's one of those things people never understand until they fall of their own accord (usually over a kerb of some kind, with low kerbs with about a 5cm upstand particularly treacherous) or crash into a pedestrian/a shop's outside vegetable stack/an A-board/over a dog leash/café chair/café table/rubbish bag, etc. I've seen all of these things happen and more. Statistically, a lot of cyclist injuries occur without any driver involvement. The aforementioned low kerbs are a source of serious injury especially for elderly people, it seems, as they may fall awkwardly. Many hips have been broken that way.
Strictly speaking, one should be comparing like for like, and it is, I think, self-evident that riding at the same speed along the footway as along the carriageway usually means a higher risk on the footway. However, oddly, riding slowly along the footway isn't necessarily 'safer', mainly because of the low kerb issue. People hit them at odd angles, they are often irregularly-shaped, and with a bit of a low-speed wobble can easily go down.
Was that on Farringdon Road, Phoenix Place, or Gough Street? The latter's cobbly, but I don't expect that's what you were referring to.
I've been trying to work out how one might go around a corner via the footway three times on either of these streets but it's not obvious to me what you mean.
In general (apart from possible site-specific reasons) people ride on the footway because they imagine it's 'safer', which it isn't. I don't think I've ever seen anyone do it specifically to go around a sequence of corners, although I've seen plenty do it for just one corner.