Have a look at the following link for some more detail Insha'Allaah:
It mentions that:
(2) Furthermore, the Ahl al-Hadīth are Ahl al-Sunnah wa al-Jamā`ah, for the Hadīth is the Sunnah and the Jamā`ah (Assembly) is nothing less than the truth. Anyone who follows Hadīth is upon the truth.
Regarding the 4 maddhabs and Ahlul Hadeeth - the two are not mutually exclusive. So the scholars of the 4 maddhabs are all from the Ahlul Hadeeth, and among the Ahlul Hadeeth are those who follow a maddhab:
... the adherents of these madhabs are from the scholars of Sunnah, and they are all from Ahl al-Hadeeth. Allah aided them and granted them understanding and comprehension, and thus they were able to merge between memorisation and understanding. Subsequently, their ijtihad led them to various views which they then compiled in various works..."
It's just a matter of terminology... the important thing to understand is that it is not some kind of new sect:
(5) It is they who shall be manifest upon the truth until the establishment of the Hour. It is by Hadīth that they become manifest and receive victory, and it is because of it that they are saved. All of these words and titles are general in a sense and specific in another. Thus, when one of them is mentioned, the others are included such that each word by itself refers to all the parties of the Saved Sect (al-Firqah al-Nājiyah). However, when the word Ahl al-Hadīth is mentioned alongside another word, it indicates that what is meant is those who are preoccupied with the study of Hadīth. This explains why many of the Salaf would use the word Ahl al-Hadīth in particular for those who were preoccupied with its study.
Shaykh al-Islām, may Allāh have mercy on him, states, “We do not mean by Ahl al-Hadīth, merely those who are devoted to hearing them, writing them, or narrating them. Rather we mean by them all of those who are most deserving of having memorized them, knowing them, and understanding them apparently and in reality, and following them privately and publicly.” [Majmū` al-Fatāwā (4/95)]
From this, we come to know the reason for the disagreement between the adherents of Ahl al-Hadīth in our time as to whether or not there is a distinction between these titles.
(6) “Ahl al-Hadīth are the Salaf from the (first) three generations and those who tread their path from the Khalaf.” [Majmū` al-Fatāwā (6/355)]
And Allaah (swt) knows best.