Yup. Lots of places in TX do specialty industrial trucks. Don't see any Rosenbauer addresses that aren't a heck of a lot closer to other ports, but not unlikely that they would contract with one of the shops here that do primarily oilfield support and brush fire vehicles. Those deal with a lot of terrain and environmental conditions pretty similar to what the Saudis are likely to want these to operate in.
I'd say that 'proximity to a port' is probably less important than 'close to suppliers' and 'factory set up to build the contracted vehicles'. Shipping is cheap, after all, even before you hit the port.
There's another factor as well. The Saudis, due to population growth and what not, are opening a couple hundred
new fire stations and emergency response centers. They ordered over a thousand vehicles. It's the largest order Rosenbauer has ever received.
Now, these trucks may not be part of that contract, but it could very much be a 'all hands on deck' type deal where 'how close it is to a port' is a minority concern compared to 'where do we have factory space to build all this stuff?'
Heck, the article mentions that 506 of the vehicles are going to be built in South Dakota, to which I ask: How much further from a port can you get?