It's a vacuum hose/tube ... still part of the PCV system ... usually CAI tubes have nipples for those hoses to be connected to.
'13 Mustang GT SterlingGray, 6-spd man, Recaros, Track Pack. Ordered 6.6.12, born 7.25.12, mine 8.11.12. 2.3L Whipple & a few other things. 591 RWHP, 505 RWTQ