Did you know Thuja can have juvenile foliage? This is one of the thuja that was in my garden and I removed it 2 years ago when I moved and its been in a pot with 100% DE since then. Now I noticed lots of juvenile foliage. I don’t know what’s causing it. I might have forgotten to fertilize this tree all this year. I am not sure.
I’m guessing it is stress related.
Other species will do this besides Junipers.