Coordinates of each point in ACAD are stored as real numbers with precision up to 15 decimal places... So to get LINE, you must specify exact coordinates with all decimals and I suggest that you use this variant :
(ssget "_C" pt pt '((0 . "LINE")))
Note you can get pt with exact coordinates by : (setq pt (cdr (assoc 11 (entget (car (entsel "\nPick LINE..."))))))
Now to check precision : (prompt "\nPOINT : ") (princ (rtos (car pt) 2 20)) (prompt ",") (princ (rtos (cadr pt) 2 20)) (prompt ",") (princ (rtos (caddr pt) 2 20))
If you have(get) those data with precision up to 15 decimal places, you can try :
(ssget (list '(0 . "LINE") '(-4 . "=,=,=") '(11 Xcoord Ycoord Zcoord)))