We can't say with 100% certainty that they are excluding SegWit transactions just by looking at the size of blocks.  We can definitely conclude that blocks larger than 1mb in size have to have some SegWit usage included, but it's entirely feasible to have a block smaller than 1mb that still includes some SegWit transactions.  Perhaps it's just a coincidence?  I saw two antpool blocks yesterday over 1mb.