Heel down...heel up...what does it matter as long as it gets the job done. Both techniques have their pros and cons and both are used either exclusively or alternately by drummers.
Jazz/bebop drummers play heel down a lot when they have to "feather" the bass but switch to heels up when they need a bit of power or speed. When playing in a soft volume situation, the heel up option may be difficult to control, volume wise.
So there is no fixed and fast rule. Use what works for you...do not copy others blindly.