Since you've looked for answers on the Wiki, it's not really a spoiler for you. The Blind Beggar is a random encounter on the road that triggers Adaon's new Companion quest, if he is with you.
For clarity, the THREE new companion quests are triggered by having your Companion with you and being Level 13+. Hirge's is triggered in any Capital and occurs as a bad feeling about her formal trainer. Griss's is triggered on the road as a random encounter by a royal messenger trying to delivery her a message. Adaon's is triggered by the random encounter your experienced , an old beggar on the road.