[quote=@Beloss]
[@Holy Grail] did you set up your summoning circle someplace weird?
[/quote]

As was said, they chose to summon at the site of what, in another world, would be known as the Tohsaka Manor. As one of the fallen leylines of the city and a place that is under constant watch, it shouldn't be much of a surprise that someone was already present there prior to the summoning.