Makes no sense at all.
Two straight promotions, 15th placed in the PL, and seemingly stable management.
Look at their last 5 results in the PL: Chelsea (A) draw 2-2; Villa (A) win 0-1; Arsenal (H) draw 1-1; Stoke (A) draw 3-3; Fulham (A) 1-1. That's an impressive 7 points from the 5 games, picking up points where they wouldn't have necessarily been expected.
Pochettino may well be a good manager, but he has no experience in English football. The chairman talked of how Pochettino's abilities as an "excellent man manager" helped motivate the move, and yet he doesn't speak English. Just to name two obvious examples, look at how that worked out for Juande Ramos and Capello.