Yes, it is strange, but 'out loud' means using one's voice; it is the opposite of 'silently' or 'in one's head'. 'Loudly' means 'in a big voice', the opposite of 'softly'. So when we are on the train reading a book, we do not read out loud; we read to ourselves in our head.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.