Hypercorrection.

I think it's historically been OK to refer to any person using they/them/their. More recently, even in progressive circles I think, it's still OK as long as you don't have information about the person's preference that would make neutral pronouns offensive to them. Basically, it's fine until you know it's not.

It's true that all the supporting pictures in the article are of women, and you're likely right that all the demonstration models were probably women. But the machine is not gender-specific, the process of using it doesn't seem like it would be gender-specific, and the author was generalizing a series of demonstrations instead of a specific demonstration with a specific model. The subject of the sentences/paragraph you're concerned about - 'the demonstration model' - is itself gender neutral. For all of these reasons I think it makes sense why they/them pronouns were used here. Not strange or controversial at all.