When it comes to vertical drilling into a joist, the internet is split in two:
One is discussions about drilling a large hole through the joist to pass plumbing/electrical/etc, and the answer is "don't do it!". There's discussions about the bending face, thirds of the joist, code, etc., and how any notching/drilling on the bottom of a joist - especially in the center 3rd - is the worst thing you can do.
The other half is about mounting stuff to the ceiling - on which there are... crickets. If you keep looking, you'll find mounting instructions for stuff (like lamps, fans, bike hangers or these 400lb and 600lbs racks), where screwing (vertically) into the joist is what you should be doing (as opposed to mounting to drywall), and as long as you're centered enough on the joist, there's nothing else to worry about. Pilot holes are welcome.
Can anyone help settle the discrepancy?
Personally, I'm mounting a 6lbs projector (+2 lbs mount) in the middle of a long timber ceiling joist in the middle of a living room; the ceiling supports a residential floor (another living room) above it. Barring new information, I've decided to use 2 x wood screws (#10 or #12 w/ 1/8" pilot hole) instead of thicker lag bolts, since those should easily support the light, static load while minimizing displacement of the joist material.