Feuding Finches

I witnessed several greenfinches and some goldfinches in the garden yesterday morning. There were several cock greenfinches and I was surprised to see them in such close proximity so close to the breeding season. Inevitably, it led to some chasing amongst the cocks. Then one greenfinch cock chased away a goldfinch. No great surprise there but then the reverse occurred. I would not have expected a much smaller goldfinch be aggressive towards a cock greenfinch.