Honest question, did you read the article? While I haven't read this particular one, I'm familiar enough with the field to know that controlling for confounding factors is one of the most basic types of controls. Any half-decent article would control for the kind of thing you're suggesting.

That said, the article appears to have been published by Frontiers in Human Neuroscience, which does have a less than stellar reputation for rigorous peer-review and, as a result, article quality[0].

[0] https://neuroconscience.com/2016/01/15/is-frontiers-in-troub...