Quote Originally Posted by Mist
Later it came to mean "a German".
Because, I think, the majority of foreigners in Russia at that time were Germans.

Just to remind of the role Germans played in Russian culture of the time, here's a list of the first presidents of Russian Imperial Academy of Science in St.Petersburg (also, think where the name "Petersburg" has come from):

1725-1733. Блюментрост Лаврентий Лаврентьевич, лейб-медик.
1733. Кейзерлинг Герман Карл, граф.
1734-1740. Корф Иоганн Альбрехт, барон.
1740-1741. Бреверн Карл фон.