The episode "The Modern Prometheus" suggests that Mary Shelly was inspired to write Frankenstien by seeing an immortal Lord Byron "die" in mid-battle and apparently be revived by The Quickening (becoming the lightning that famously animates her novel's creature). However, the method of lightning to reanimate dead tissue was invented for the films, not the novel.
Mary Shelley's actual inspiration for Frankenstein came from propaganda being spread about Charles Darwin, and a French translation of a German horror tale, Les Fantasmagoriana.
This is a historical error. In the world of Highlander, Byron is an immortal and immortals are unable to procreate. The real Lord Byron fathered at least 3 children. He has many living descendants through his daughter, mathematician Ada Lovelace, who herself has been recognized as the first computer programmer. This fact seems to have been forgotten or omitted by the writers. A mention and possible explanation should have been made.