Nothing weird about multiple people gaming together to be holding the same device at the same time. Also nothing weird about people turning to look at a camera that is about to photograph them.

Put the two together and you'll likely get what we see here with these Barcelona players.

Not one of whom decided to buy a grey switch.

Cool! :) Most likely Nintendo sent them these machines. Heck they should do this more often. :D

Perhaps Nintendo provided them to these players? Maybe they bought them so they would match? There's also a chance their staff purchased a bunch of the same type of Switch in a single order and put them in these players' transportation for their entertainment?

It's up in the air, really, but I would think Nintendo would make sure to include both varieties, the gray one and the colorful one so as to advertise both variants of the Switch but this does not seem to be the case...

Hmmm, here's an idea for a commercial. Messi playing FIFA 18 on the Switch at home, then getting a call from the club manager or someone, then he takes the Switch on the plane, keeps playing. Fast forward to just before the game and Madrid, keeps playing, then shuts it off just as they're heading out. Fast forward, does his thing on the field, comes back, starts playing again. Then he looks at the camera and says: "Haga el interruptor." (Make the Switch).
Cuts to Nintendo Switch-FIFA 18 bundle on a shelf for $300.

Probably get arrested for the tax owed on the marketing deal when that ad airs.

Probably with FIFA 19 if you're suggesting a price cut + bundle. There's no sign of them needing a price cut at the moment for this year. Though that ad would be cool to have.

Oh Damn, that's right. 
When does that deal expire?

Oh nice!

Smells like paid marketing to me. *sniffs deeper* Yep, paid marketing.