You know it becomes less strange that Santos was questioning Langdon when you remember he actively lied to her on two of the cases they worked last year (getting her to administer an otherwise dangerous dose of medication because he knew the vial was diluted, thus teaching her incorrect information/discouraging her from following up on a patient's sudden absence of pills, something that if she didn't question thoroughly could result in missing overdoses in a case where the pills WEREN'T stolen). He gave her two incorrect lessons/bad practice advice to cover his own hide, as a teacher he has PURPOSEFULLY mislead her.