It's not an uncommon tactic to give homeless one-way tickets to other cities. In fact, San Francisco actively does it as well [0]. It doesn't seem like San Francisco and cities like it are particularly targeted for this kind of activity. The only case I can recall is in the case of Nevada intentionally sending mental patients to SF which was settled out of court[1].

[0] https://www.theguardian.com/us-news/ng-interactive/2017/dec/...

[0] HN discussion: https://news.ycombinator.com/item?id=18375280

[1] http://www.sfexaminer.com/sf-reaches-400k-settlement-proposa...