That doesn't strike me as particularly dumb. It's pretty easy to print out a fake driver's license (or use someone else's) that's going to work fine getting into most bars, and the risks of getting into legal trouble for attempting to use a fake ID to buy alcohol are probably pretty similar to the risks of using a fake vaccine card, and yet most people don't argue that that system is a dumb way to enforce the drinking age (ignoring whether the drinking age itself is a reasonable policy).