They simply don't specify everything on patch notes. Examples would be: they stopped posting pictures for map changes, didn't write that corner boosting would get a new audio cue, many bug fixes are just silently done, doorman's improved door placement was pushed before patch notes, etc.
I'm not saying that this case (Viscous) is intended, it may well be an oversight, it's just that not mentioned doesn't equal unintended.
Why does intentionality matter anyway? If they are ok with inconsistencies like parrying puddle punch, inconsistent, unintentional interactions are totally fine as long as it's balanced. I personally like consistency in a way that punch can't be parried and walker can't be stunned at all, but my opinion is not important if everyone likes those inconsistencies.