I understand it as it follows:
Fusarium lives around the plant in every environment. At least as spore. Soil, leaf, twigs, buds. There are also many species and varieties of fusarium yet to describe. Anyway, it can't enter in the mango by itself. Spider mites provides the microdamage necessary to let the fusarium enter in the plant, wich lately leads to damaged growt because the ormonal imbalance.
So you can do two things: treat the spider mites, or treat the fusarium.
I haven't understood yet why they seems to suggest to cut the branches: this could give a relief, but won't eradicate the disease.
On that site they suggest mainly treatment for spider mites (i checked some of the products suggested for treatment). I'm guessing I'm going with these before starting to prune, and i'lll see how this patology will go. Even because, at first sight, fusarium isn't easy to treat.
(I also have had antrachnose few weeks ago but it went away with a little copper, so i tought this malformation was cold and antrachnose related)