Any other ideas?

I was performing a home inspection at a home which had water intrusion in the basement about 7 months ago. It was never repaired properly and the humidity in the basement was around 67%. Mould was evident throughout. However, I found one strange phenomenon in an old cistern. There were a number of frozen waterfalls on the walls. The foundation had no issues and there was no apparent source of the water. The only thing I could think of was that the excessive condensation froze to the wall. If anyone has any other thoughts I’d like to hear them. There were no plumbing pipes in that area at all.