Yeah that seemed most likely to me too, but as tonybeldig pointed out, Mazda seem committed to highly efficient ICEs as their means of reducing CO2 emissions. Their website even advertises their cars as 'more efficient than most hybrids' or something along those lines, so they'd certainly have to change their message if this is a PHEV.
However the design language and the logo certainly are very Mazdoid.
edit: here is the line about the CX-5 from their website: '
CX-5 that boasts best-in-class EPA-estimated 35 highway MPG, better than all other SUVs—even hybrids'