Yechezkel prophecizes about the vision of the future Third Temple and future State of Israel. The book of Emor discusses the laws of the Kohanim and the laws of the Kohanim's conduct in the Temple during their service. That is why we read the prophecy of Yechezkel (ch. 44) regarding the Third Temple.
Yechezkel prophecizes not only about the actual Third Temple, but also about the laws and restrictions pertaining to the Kohanim at that time.