Your neighbor forgot to tell you he pulled the trigger.
I have owned several Glocks in my life, I have accidentally dropped my loaded Glock 23 twice in the last 20 years, it never discharged.
There is only one way a Glock discharges by pulling the trigger, unless is in need of repair, send it to Glock for repairs.
:-). That could be I suppose. He didn’t say he dropped it. He said he picked it up and it went off. He probably hit the trigger by mistake. I’ve only personally been around two, my sister’s and the one my husband traded for. He said the trigger pull on his was so light that it made him very nervous so he got rid of it. He prefers his 9mm Ruger. My sister does OK with hers because she practices with it all the time but she will be the first to tell you that the trigger is too light for most people. I prefer a stronger trigger pull myself.