They ate the Passover "other than the way it is written" (30:18). Was that wrong? And what does the chapter say happened?

The chapter tells it in its own words and adds no more. "For a multitude of the people, even many of Ephraim, Manasseh, Issachar, and Zebulun, had not cleansed themselves, yet they ate the Passover other than the way it is written" (30:18). It calls it what it was: not as written. Then it says that Hezekiah prayed for them: "May the good LORD pardon everyone who sets his heart to seek God, the LORD, the God of his fathers, even if they aren’t clean according to the purification of the sanctuary" (30:18-19). And "The LORD listened to Hezekiah, and healed the people" (30:20). The prayer names who it asks pardon for, "everyone who sets his heart to seek God" (30:19), and the chapter gives the LORD's answer without saying more. Numbers 9 had told of men who "were unclean because of the dead body of a man, so that they could not keep the Passover on that day, and they came before Moses and Aaron on that day" (Numbers 9:6). They asked, "Why are we kept back…?" (Numbers 9:7). These notes set the two side by side and add no verdict of their own.