Corbyn was famous for organizing large rallies, if anything this was a criticism of him - he was much more interested in rallies and protests than leadership.

Pictures of Corbyn in front of huge crowds at rallies:

https://labourlist.org/2019/08/corbyn-encourages-labour-mps-...

https://www.counterfire.org/article/letter-left-corbyn-labou...

https://socialistworker.co.uk/news/thousands-rally-for-jerem...