An interesting article on Autumn Migration in Big Cities in the Autumn 2016 Bulletin of The Cornell Laboratory of Ornithology.
The article states that migrants are "highly likely to pop up in a dense urban area during fall (autumn) migration"
Although this is based on data from North America, there is no reason to think it doesn't happen here also - and Homantin is a good example.
Why this should happen in autumn rather than spring is a good question. I would guess it has two factors - the number of inexperienced 'first-winter' migrants in autumn, and the slower pace of birds on autumn migration than spring, when they fly longer distances in each spring migration step rather than in autumn.
