Birds of a feather...?

We have a pond with a waterfall in our garden and we enjoy a large variety of winged visitors throughout the year.

However, yesterday something quite different happened and we were wondering if anyone could explain it, or has had a similar experience.

It was about 7am and I was looking out of the bathroom window when the garden was suddenly alive with a large flock of many different birds.  They stayed for around 10 minutes, dipping in and out of the water, and during that time we observed:

Quite a few goldfinches (about 8 or 10); a single bullfinch; a pair of song thrushes; a blackcap; a pair of coal tits; dunnocks (a pair, I think); at least one wren; and a robin (although I think it may have been our resident robin just checking out the commotion)

The strange thing was that they were clearly in the same flock - they all arrived at the same time and left at the same time

It was delightful to watch, would love to know how common (or otherwise) it is to see so many different birds flocking together.