Do you know how you created that qza? Are you sure it’s a SampleData[SequencesWithQuality]? If you are not sure you can check via qiime tools peek ok70_demux.qza.
The issue here is q2-quality-filter and q2-deblur cannot use paired-end data unless it has already been merged/joined. If you look at our pending release notes for the upcoming 2017.11 release, you’ll see that we’re adding support for joining your paired-end data. So you should have some options available soon!