I long suspected that a Rebbe of mine made up gematrias as he went along (after all who can mentally add up the gematria of a possuk and challenge him). I once whipped out a calculator and started adding up the words he was quoting, he got all defensive and said “put that away, this is Limudei Kodesh, not Limudeo Chol”.
The moral of the story, I believe, is that people feel they will have more credibility if they quote something that more than 99% of the population will not be able to refute on the spot.