Maybe a little bit biased (I'm Serbian), but here's the best explanation I can give you. Bosnia was, for the most part independent. In the early middle ages, when the Slavs first started migrating there, the smaller tribes Dukljani, Travunjani, Zahumljani, Neretljani etc. would ally together to create strong alliances, and later states, Rascia, Serbia's predecessor was basically founded this way. This was more or less the area around today's Montenegro, Western Serbia and parts of Bosnia. To my understanding, Croats mostly kept to the parts a bit further north, not integrating into any tribal alliance until entering an union with the Hungarians, though they shared many cultural traits with the other tribes (the Croatian, Serbian and Bosnian languages are even today essentially the same). Fast forward a little bit, when the South Slav countries were a little bit more established and developed, we see that at the time of the battle of Kosovo (where people of Bosnia participated), Bosnia isn't under the Serbian or Croatian rule, but is instead ruled by Tvrtko, a man who's father was a Šubić, a Croatian royal family and mother was of Nemanjić, Serbian royal family, blood. The population of Bosnia back then, was as far as I know, catholic, though later, a man from the noble house of Kosača managed to take control of the southern part of the country taking for himself the title of The Herzog of st. Sava (St. Sava or Rastko Nemanjić is a Serbian Saint, not really worshiped outside of it), thus creating the short-lived independent Herzegovina.

All in all, they were people of mixed Croat and Serb descent living in an independent country up until the Ottoman conquest.

There is an very interesting article (unfortunately in Croatian) about the borders of the medieval Croatia during the king Tomislav here: http://povijest.net/povijesni-zemljovidi-i-granice-hrvatske-u-tomislavovo-doba/. It is basically a criticism of the maps in the current Croatian elementary and highschool textbooks. The author (he is a Croatian historian) says that the real territory was probably smaller, and only some parts of Bosnia and Hercegovina was part of his kingdom. Read the full article for more, I'll just cite a few sentences:

"Za ovu problematiku najvažnije je 30. poglavlje koje, kako je dobro znano, čini svojevrstan izuzetak cjeline kao nešto kasniji rad anonimnog kompilatora.(35) Spomenuti autor donosi popis hrvatskih županija i gradova. Županije su nabrojane ovim redoslijedom: Livno, Cetina, Imotski, Pliva, Pset, Primorje, Bribir, Nona, Knin, Sidraga, Nin, Gacka, Lika i Krbava. Za posljednje tri anonim posebno naglašava da njima upravlja ban.(36) U gradove “Krštene Hrvatske” car pisac ubrojio je Nin, Biograd, Belica, Skradin, Livno, Stupin, Knin, Karin i Klobuk. "

In short: The 30th chapter of "De administrando imperio" (https://en.wikipedia.org/wiki/De_Administrando_Imperio) lists Croatian counties and cities. You can get a clue of how Croatia looked on the map by this list: Livno, Cetina, Imotski, Pliva, Pset, Primorje, Bribir, Nona, Knin, Sidraga, Nin, Gacka, Lika i Krbava. Za posljednje tri anonim posebno naglašava da njima upravlja ban.(36) U gradove “Krštene Hrvatske” car pisac ubrojio je Nin, Biograd, Belica, Skradin, Livno, Stupin, Knin, Karin i Klobuk

Most of those cities are today in Dalmatia and Lika. I don't know about Pliva (today Pliva is a river in Bosnia near Jajce) and Pset. But the rest are almost all in what is today Dalmatia and Lika. Except Livno (Bosnia). Judging by that, the answer to your question would be -- no. The medieval Croatia was mostly Dalmatia and Lika, without Zagreb, without Slavonia, and definitely without (most of) Bosnia.

Note also that, later, the territory of the medieval Croatia was conquered by the Bosnian king Tvrtko (that's why he claimed the title "King of Croatia"). So, the total opposite was true for a short period -- Bosnia owned Croatia.

PS. Of course, I may bi biased, so just to be clear: I'm part Croatian, part Slovenian, living in a county which is today in Croatia but was never part of medieval Croatia (Istria), in a town which was Venetian for 7 centuries, and my Croatian ancestry is from Duvno (near Livno, one of the towns listed above).