I think these two questions are unrelated. But as they present you with the idea for one post/thread, I suppose there is the possibility that somewhere in the context there is play on the two words flag [='flag-stone": a paving stone] and paving-stone. (There is no useful word-play in the part you have quoted, but I wonder if your two related questions are related by something in the context.
I've never heard of someone 'stitching himself into a flag', but - with the sense you suggest - people are often said to be 'wrapping' or 'clothing ' themselves in a flag.
'They carved paving stones for the streets' means just that. A reason for the carving might be to give a tree's roots room to be fed and watered.