I second that @nakamura12. If this story was indeed true and OP is genuine with his intentions, I am wondering why it took him quite the time to decide to finally send back the mistaken tip. Also, he should be aware that no one actually believes anything impulsively without seeing some receipts or evidences of such subject or event. On top of it all, there is an existing accusation of him about being a notorious scammer through begging for tips kind of techniques. We all should be careful about such things.
Well if the evidence is complete then I am ready to give this forum user a negative trust for begging scheme. Maybe the 3.8 btc is received through begging of tips. I also wonder why that kind of amount is tipped. My guess would be that the btc price that time is low and it is less than the amount in usd compared to now. It could also be a way to earn merits by doing a so called good deeds by telling people to return the tip. It took a long time to decide to return the tip so this is most likely fake.