Looks like the bark is split. The worst thing for a citrus tree is to have the sap start flowing & then a hard freeze.
Looking more closely, I don’t see any bark splitting yet. But yeah, this freeze was real rough on everything (even native stuff — a big number of our live oaks and other natives are really brown) because we had been mostly in the 70s and even low 80s for a couple weeks before the freeze. There wasn’t a gradual cooling, either. The weather in the high 70s since then has really brought all the freeze damage out to the forefront.