Explain to your Dad that your address was not posted publicly. Explain that it is not anywhere where someone else could see it, other than the individual with whom you are exchanging gifts and the person who organized the swap. Invite him to visit Pet Talk, so he understands that it's not a "chat" place, and that your address is not visible.

Then explain that you would never go to meet anyone you met online without their permission, or without one of them accompanying you, and that you understand he is worried, and that you will be very careful.