There have been a couple contradictions, clarifications, and confusions regarding the horse and pony write-ups over various entries but I've not seen this one addressed in any of the errata or online materials.
As per the Bestiary-P117 the standard "light" horse has a Str 16 and the advanced "heavy" horse gets a Str 20; however according to the Core-P174 their carrying weight thresholds are 175-525 and 229-690, which if worked backwards yields Strengths of 14 and 16. [I'm assuming this is a holdover from 3.5 stats and that their CWTs should be raised to 229-690 and 400-1,200; but both the PRD & Errata for the Core reference the lower values so I wanted to make sure I wasn't missing something.]
And since I have your temporary attention and we are discussing horses; is there a reason why the standard "light" horse had its speed knocked down from 60 to 50? I can understand the heavy horse being slower, but it seemed appropriate for the light horse to be faster (and also very efficient mechanically for it to move twice what a typical speed 30 person did). I'm almost certain it even started that way, and then got errata'd back; just curious.