Truthfully, we will probably never completely know the truth, but there is no substantial evidence to prove that he did not. Finding out otherwise would deface the homages performed in Portland in his honor. Therefore, I would like to believe that yes he did play in Portland before he died.
Buddy Holly probably played in Portland on October 22. He was listed as Bud Holly and the Crickets in the Oregon paper in an article previewing the concert. The plane crash was noted in the Oregonian on 2/4/59, and he was referred to as Buddy Holly who played with the Crickets. Plus Portland has paid homage musical homage to Holly over the years.
I think it is a true that Buddy Holly performed a show in Portland before dying. It was on the 22 october of 1957. But it has been so long that just some newspaper articles remain and some memories from people around that time. I'm sure it could be remembered as a great show.
Buddy Holly died before the concert in Oregon. While there are some strange coincidences, that is all they were: coincidences. One of the coincidences was the Oregonian mistakenly called the Crickets' lead singer "Bud Holly" in a preview of the show at the old Paramount Theater. This was nothing more than a mistake and people think too much into it.