Rust Skyportal

Me and some friends was playing Rust and suddenly we saw something looked like a portal in the sky over the sea, and it got bigger and bigger then it got smaller and disappeared!

It looked something like this, just without the smoke effects!

Secret/Easter egg?

We tried to look after it again so we could take screenshot, but it did not come next night.

have been there quite some time , as far as i can rembers since i started playing. nothing special