Temperatures aren't a random number you get from throwing 10 dices and adding the numbers. This isn't a statistical issue
Let's compare two scenarios: (1) no warming and (2) warming.
With no warming, when a heat wave hits we get a few new highs. This is because (a) heat waves a rare events, so we may not have one in the record for that exact day and (b) due to microclimates in the area, the exact conditions will affect which sites are able to beat the record. And (c) there aren't that many records to compete with.
With warming, problems (a) (b) and (c) still apply. But you get a nice little bias up which should increase the number of sites obtaining new records. Yay except... the amount of warming so far means that it won't be a complete wipe out of new records, but rather just "more."
The question is how to distinguish the two cases. How do you tell if it's just the expected number of records being broken vs an increased number? The answer is stop doing that! Instead we should look at all daily temperatures -- rather than focusing on the count of record breaking highs -- because then we have a lot more data to work with.
In any case, the PNW heat wave does not match any reasonable expectation for the types of records we expect to be set by global warming because records would have been smashed regardless of warming.
None of this argument is an "anti-global warming" argument. Too many people conflate "science says this particular event was not a sign of warming" with "this person is a climate denier." If we're going to follow the science, that means less panic over individual events and more concern over the ongoing changes.