No. Pomerelia was one of the constituent parts of Royal Prussia. The latter has been established during the Second Treaty of Thorn ending the Thirteen Years War (1454-1466) and causing the Western part of the Teutonic Order lands being ceded to Poland with the remaining areas remaining with the Order, formally becoming vassal fief of the Polish Crown.

The extent of the Royal Prussia as of 1466 covered Pomerelia (pol. Pomorze Gdańskie, ger. Westpreußen), areas surrounding the cities of Malbork (ger. Marienburg) and Elbląg (ger. Elbing), Chełmo and Michałów Land (pol. Ziemia Chełmińsko-Michałowska, ger. Kulmer und Michelauer Land) and Warmia* (ger. Ermland). These four areas would eventually become, respectively, Pomeranian Voivodeship, Malbork Voivodeship, Chełmno Voivodeship and Duchy of Warmia, ruled by Bishops of Warmia as ecclesiastical vassals of the Polish king.

Pomerelia was basically synonymous with the Pomeranian Voivodship established in 1454, i.e. the entire part of Royal Prussia located west of Vistula with the exception of the northernmost part of Żuławy region extending into the Vistula Spit that belonged to Pomeranian Voivodship (Pomerelia) and were located east of Vistula. This should not be mistaken with modern Pomeranian Voivodship that reaches farther west but does not cover some of its former southwestern area now located within Cuyavian-Pomeranian Voivodship).

The area of Pomerelia has been extended in 1637 (20 years before the province has effectively been lost due to Polish-Swedish War) after the Polish Crown claimed the lands surrounding the cities of Bytów (ger. Bütow) and Lębork (ger. Lauenburg), after their last owner from the local Gryfita family died without a heir.

So to sum it up, Pomerelia was essentially a westernmost part of the Royal Prussia, constituting roughly 60% of its area and almost in its entirety located to the west of Vistula that formed its eastern border.

*It is an interesting question itself, why such names are transcribed into English in a way that makes proper pronunciation much less obvious. In any case, the 'w' in 'Warmia' is pronounced as 'v'.