First things first. I haven't done a thing and haven't been asked to help out. The guy hosting the event thought we were still working together. This DJ I know personally that is doing the event again.Yet you were willing to supply a sound system to a DJ in a park (for free) so that it sounded right (got the job done).
I don't know who this DJ is doing this event in the park. So why would I help that DJ out? It's not my fault this DJ doesn't have the gear to work with. Especially someone else I don't know asking can someone supply a sound system for free or near free. Trust me I don't do many free events. Just on occasionally bases.