Don't forget - Ryan has a large streaming video business. In fact, that is probably his core business - and selling trees is a sideline. When he has his annual sale,
he sends several emails out to all of his subscribers, so he already has a personal relationship with his core target audience.
Additionally, once a year immediately after the sale he drives a truck across the country, dropping off trees along the way. For many people east of the rocky mountains, it provides a convenient and relatively low-risk way to have a large tree delivered.
Finally, as
@rockm pointed out, some of these buyers may be Ryan's students, or members of local clubs. For all we know, they may have seen these trees in person and known they wanted to buy them - totally aware that they would do well in their local environment.