You're missing the point of why these guidelines exist: to prevent the tiger from escaping and hurting somebody. Recommended height is 16.5 feet, because tigers can potentially clear something lower. You can get away with something lower if you do something else to limit the tiger. In this case, the SF zoo had a moat. Ever tried jumping out of a swimming pool? The water really limits how far you can go.
The SF zoo's moat was unfilled.
If the tiger got out, the enclosure was ipso facto substandard and inadequate.
That is the most damaging bit of information. If a water-filled moat wasn't necessary, why did they have the moat?
Not to argue the issue regarding inadequacy, but the fact that the tiger got out has no bearing on whether the enclosure was substandard or not. The standards are defined independent of the actual behavior of the cat - with the intention that following the standards would confine any enclosed cat.
I would agree that the animal’s escape is indicative of an inadequate enclosure, but do not know whether or not the enclosure itself was within the guidelines for such pens.