It's just not rational to think 'ah yes this level of walk rate from these relievers was clearly foreseeable'. And the diminishing stuff bit is largely a post-hoc justification and not even particularly true, Pressly's velocity is the same as it was last year, Pearson's is higher!
Sometimes weird stuff happens in small samples, especially when you have an abnormal calendar to start the year and you're facing a bunch of good offenses in a row(note that BBs were not a problem against the A's). Sometimes the bad stuff will continue, I'm concerned about Pressly not missing bats on top of the walks. But not every upsetting day from the pen(or the offense, or a SP) has to be proof positive of a structural issue.