It is. All Guyanese who are born in territory claimed by Venezuela are citizens of Venezuela by birth and are entitled to Venezuelan papers upon application. The Essequibo is as Venezuelan as Caracas in Venezuelan law. I have a personal friend who was on a trip to Caracas in the 80s and decided to get his Venezuelan passport and other state papers as a lark while there. They did not even care that he spoke not a word of Spanish. And he never had any desire or intention to ever live in Venezuela.
So yes, there are possibly hundreds of thousands of Guyanese who by operation of Venezuelan law are citizens of Venezuela by birth or descent.