The first one is a union, because wherever x is in the 2 intervals, the inequality is OK.
It may be in either the first or the third interval, it'd work. The union is quite equivalent to "or".
For the second one, there's no union, because it's a single interval, there's no need to make a union with another interval...
For the inequality to be verified, x has to be in this single interval, and not outside it.
I don't know if it's clear enough , if it helps a little, ok, if not, I'm sure someone else will tell you something else