Someone is genuinely helpful or generous, but thinks or misremembers that they were a lot more helpful and generous than they actually were.
Say someone loaned or gave you $1,000 and now remembers it as having been $10,000, and makes occasional references to that higher amount. Or something similar.
Do you correct their mistaken impression or memory?
On the one hand, they did you a serious favor and it seems like poor form to try to minimize it. OTOH, it can rankle just a bit.