Just walking across a circuit board is not enough to cause a lead toxicity in any species. Ingestion of lead is harmful in all species.
Circuit board from what item? There's been a big push over the past 3 years to do away with lead based solder. Not sure about your particular board.
Lead is always dangerous but I don't believe the very brief contact he may have had from walking across the board would cause too much exposure. If he was chewing on it, that's another story.