It's about as standard procedure as crossing your legs when you're sitting.
Arms in microgravity, without conscious effort to keep them by your body, will tend to extend the elbows to the sides - just like holding knees together when sitting, at least for men, requires active (if minor) effort. Holding arms like this simply prevents sticking elbows into the person next-to, and takes less effort than actively squeezing them along your body.
Compare to these:
For many astronauts, it is simply a matter of being considerate to your fellow astronaut who is appearing alongside you. It would not be nice to let your arm drift into contact with the other astronaut - astronauts have "personal space'" too.
Plus, I think we'd all agree that Earth-bound humans by and large think the natural position that arms want to attain in microgravity conditions looks "sort of dumb."
Astronauts have egos, too!
There is no special procedure there - just microgravity.
Note that the one on the left looks like a normal relaxed pose, with his arms dropped down as they would be on Earth.
The other two do look a little "unnatural", but if you ignore their arms being pointed forward, it is exactly the same pose, and just as comfortable with no gravity pulling their arms down.