[@Kouki]
Actually, Erik can only sense particularly strong auras without trying to (such as those of magic users, or someone from another plane of existence, for example), and while it might be possible for him to focus on his aura sensitivity to be aware of the auras of less abnormal individuals, his feeling of being watched was just heightened senses and his decade of training among the Alfr!

And yeah, I can definitely see why being noticed while trying not to be would put someone like Holden off (although the fact that the person who made him very plainly recognized and respected his desire to not be seen, by not only not actively pointing him out, but by even making their acknowledgement of his existence as miniscule as possible, seems like it would do a bit to help at least reduce that!)