It is possible that a warrant was in fact issued years ago but for some reason not executed at the time of your friend's release from prison in AZ; mistakes happen. He should let his attorney know where he was at the time that WA charged with a new crime. There should be records to show that he was incarcerated out of state, and there may be records that show the warrant was received by AZ authorities but not executed. He should not be facing additional time for failure to appear if it can be shown that he couldnt comply with an order to return to the jurisdiction because of his incarceration.
"FTR" in WA usually means "failure to register" which isnt a Class A felony here. It seems unlikely that a warrant for a class A felony would have been missed as those are essentially life count charges, and deemed the most serious of charges in WA.
If the warrant was for a class C felony, it is possible that Washington knew he was in Arizona but chose not to extradite him. It can be costly to move a prisoner long distances, and sometimes the state with the warrant will choose not to bear the cost. If it had been a class A felony, Washington almost certainly would have paid the cost to extradite. In the end, the responsibility to deal with the warrant always lies on the person the warrant is against.