You have heard the saying "the clothes make the man", no doubt. Though in modern times this has changed to a great degree, with individuality of expression being emphasized, in Shakespeare's day you dressed "right" or not at all.
The well dressed Victorian gentleman would dress according to a prescribed way. He would wear good quality leather shoes, typically made to order; stockings, or at the very least wool socks, covered the legs from the shoes to the bottom of the pants; a coat of a certain length hung down the back; a cane or walking stick; a hat perched on his head; etc...
These rules were only flaunted by the very poor, who shopped in second hand stores, or "outlaws" who would dare to change the styles, or have no "style" at all just throwing on clothes for comfort or to suit their own personal taste.
Therefore these characters in Acts 2 scene 7 are dressing in a way that differs from the "norm." They don't necessarily have on masks, as the term "outlaw" conjures to the modern mind, they are just noticeably different.