We reached out to Mr. Cameron and it turns out his donation was not out of the blue.  Via email, he said he'd met Chief Oren Lyons, honorary chairman of the team, at a meeting of the UN Permanent Forum on Indigenous Issues and discussed some of the "themes and thinking behind Avatar" with him and various other Native American leaders.

From Mr. Cameron's email:

Chief Lyons talked at length about their lacrosse team... how good they were, and what they represented to the Iroguois Nation and other first nation people.  I played lacrosse as a boy in Canada (not very well, to be honest), and so have an appreciation of the game, as well as of its cultural origins.  Lacrosse was created by indigenous North Americans and later adopted by European colonial cultures.  Chief Lyons was proud of the fact that his team would be travelling under their Haudenosaunee indigenous nation passports, which they have been using for 20 years.  He contacted me to tell me that they had been held up from in NYC from flying to England, and needed financial assistance to stay there, until it could be resolved with the State Department.  I jumped in to buy them a couple of days.  State Department apparently came through in time, but of course we are all shocked and deeply disappointed that England then chose to stonewall the team's hopes and dreams.  I hope this can get sorted out, as we all want to see them play.

What a stand-up guy! Though we'd be remiss if we didn't point out that this whole problem could easily be solved by the flying dragons in Avatar.