The word "they" may refer to Solomon's merchants. However this sentence is not about what the merchants did, but about where Solomon's horses came from. Alternate translation: "Horses were brought to Solomon from Egypt and from all the lands" or "Solomon's horses were from Egypt and all the lands"
The word "all" is a generalization. Alternate translation: "from many other places" or "from many other countries" (See: [[rc://en/ta/man/jit/figs-hyperbole]])