Tough to say but could be. It is also late in the growing season so any number of ailments could cause premature leaf drop.

If you stick your fingers in the soil by the trunk is it dame or dry?

What is your watering schedule like?

Main thing is looking at the dirt in the original soil ball to see how damp or dry it is. Tree will be either too wet or too dry to be going yellow from the inside out like that. If original root-ball is field or potting soil that is resisting re-wetting or shedding water to surrounding natural soil frequency of watering will be secondary.