Hmm, I'm not certain I'd make that claim. The wiring diagram does not specify what the input protection should be. If anything, from reading the instructions I see it as 120 V @ 20 A or 240 V @ 30 A. And if it needs 30 A at 240 V, then a 20 A breaker is certainly not sufficient.
Also the question would be is the 30 A what it draws or what the input breaker is supposed to be? NEC requires permanently connected devices that are designed for continuous usage to draw no more than 80% of the current provided by the current limiting device. In other words, you are limited to 16 A off a 20 A breaker, 24 A off a 30 A breaker, etc. For example my spa control panel tech notes explicitly break out actual current draw in X configuration vs appropriate breaker size.
View attachment 385621
It's very nice that your spa manual goes the extra mile and explains that a 60A breaker is only rated by the current NEC for 48A continuous duty. Anybody doing their own electric work should understand that anyway, as well as understand all of the derating requirements that are included in the NEC, but it's nice that the spa manual explicitly states it for those that do not know about it.
Looking at the pictures provided with a bit more time than I took last time, it looks like that is a 115 V only pump. Therefore I suspect that this tub was only set up for 120V
It LOOKS like when on 120V power there is a 30A main fuse in the tub. When you convert it to 240V, the one leg that gets dedicated to the pump gets a 20A fuse on it.
Since it has a 4KW Max heater on it, you are looking at 33 amps draw on that heater.
Looking at it a little more, it looks like it is also a "plug in" spa, which technically has different safety requirements (which is a load of junk, electricity is going to do what electricity does, regardless of if you can remove a plug or not)
I guess the overall story is:
They need to find the actual power requirements for this tub
They need to install an appropriately sized breaker for those requirements (keeping in mind derating requirements)
They need to have the appropriate GFCI protection
While there is usually no requirement for a line of sight service disconnect for residential units, it is still a good idea and cheap insurance
While there is usually no requirement for a bond halo for a hot tub, it is still a good idea and cheap insurance.
They need to have the correct size wire for the breaker that is installed (Again, derating as necessary for conduit fill if necessary, or for other applications)
They need to have the correct enclosure for the breaker correctly installed