Now who did this?

Someone not only got access to my wifi but also somehow changed the the led banner text. The crazy thing is that the guy who installed the led said you need a specific software to to change the text and this "hacker" supposedly did this with a phone(I'm guessing this person wouldn't have been standing with a laptop on the sidewalk). If the person who did this is reading this, good prank bro. I'd really like to know how you did this though