Indeed, it only says delfs. It seems as though there is no such specific guidance for celf's agoraphobic behaviour in the docs, unless one is supposed to draw from the mention of agoraphobia as experienced by delfs, and apply it racially. (But in reverse.)
The current docs for celf's actually say..
The elven population in cities is in a state of constant flux, as various tribes move in and out, die off, go into hiding, move into other parts of the city, or otherwise simply move
Which to me appears to indicate that celf's can and do, leave their cities, in order settle in others. As it clearly differentiates between moving to other parts of the city. It goes on to say the nomadic interests of celf's can include:
domination of the other elven tribes nearby, great wealth, presence in every city
Note that it doesn't say other city elf tribes, just elven tribes. And it clearly states presence in every city which would obviously require travel between them.
Honestly we could debate all day but it won't matter until staff prescribes a set of examples and rules that define the scope.
The docs however, in present form, do not at all suggest it's unthematic for an elf, city or desert, to leave the area they are most familiar with for specific reasons. So long as these reasons are of benefit to the tribe, and in the interest of it's expansion and success.