I finally received a copy of the Word Biblical Commentary Volume 13. Here is the context of that quote from the section discussing 2 Kings chapter 10 on page 129.
"18 Jehu's attempt to rid Israel of Baal worship constitutes the second thrust of his revolt, a religious purge. The episode is again characterized by its portrayal of the ruthless deceit of Jehu (Hebrew words) "Ahab served Baal a little." This might well be an accurate description of Ahab. Although he did build the Baal temple (1Kgs 16:32), he also named his sons Ahaziah and Jehoram, names that bear the divine name. However, the point cannot be pressed since the biblical verdict on Ahab is far from flattering (1Kgs 16:33). Jehu's statement is born of his deceit. If the Israelites had thought that Ahab was apostate, Jehu wished them to believe that he was far worse.
19 (Hebrew Words) "for a great sacrifice." This is a clever play on words on the part of Jehu. While the term (Hebrew word) generally means "sacrifice," it is also used of the "slaughter" of apostates (cf. 1 Kgs 13:2: 2 Kgs 23:20). The writer's comment concerning Jehu's intention also contains a sinister pun on the homonyms (Hebrew word) "to serve" and (Hebrew word) "to destroy.""
Later he has this to say:
"23-24 Jehu's actions are hardly commendable. The deliberate way he sets up the worshipers of Baal for extermination gives a chilling view of his character."
From this I conclude that he was using the normal meaning of the term apostates and was referring to worshipers of Baal specifically. He doesn't seem to be endorsing the loaded language that is used by the Watchtower Society when they speak of apostates. He is also critical of Jehu, which contrasts with the way the Watchtower Society praises him and almost treats him like a hero.
I thought it was interesting what 2 Kings 10:31 (KJV) says, "But Jehu took no heed to walk in the law of the LORD God of Israel with all his heart: for he departed not from the sins of Jeroboam, which made Israel to sin."
By Watchtower standards, Jehu was also an apostate.