You’re right, the bus ride from POFQ to DHS is not very long, nor is the boat ride from DHS to Swan/Dolphin. It’s just that sometimes, if you just missed the bus and/or just missed the boat, you could add 20+ minutes waiting for the next, or a total of 40+ minutes for the trip if you just missed both of them. (Of course, the walk from DHS bus stop to Swan/Dolphin is quicker than waiting for the next boat.)
But that’s why the recommendation is to allow 90 minutes for the trip. You did great and made your dining reservation on time, but I don’t want others reading this thread to think that it always works out so well.