You first tried to dismiss other sat systems and whatnot because they weren't in cycle computers, but now you post a link to a frigging watch? Yes, a barometer in a watch is a cheap way of getting altitude data - especially as it probably haven't the space to use that many different GNSS systems.
Yes, that watch (in 2017) uses GPS (not Galileo, Glonass, or anything else), so it can be hard for it to receive enough sat signals to get a precise altitude. If you have a watch/cyclecomputer/whatever that uses more than one system, it will have that many more sats to connect to, improving measurements immensely. 2017 is ages ago in the smartwatch "scene".