There is nothing in Arabic like "حالوا"
but : حلوى = Halwa = sweets
except if the person talking to you meant something else like imitating the English "hello" in a funny way
also "حالو" in Arabic dialicts comes from "حاله" which refers to someone's state
"كيف حالو" = "كيف حاله" = "how's he doing?"
It would be much easier if you could give us the context in which the word was mentioned dear sister