Yes, I think you are right. VCC and GRD a FC was connected through was outputting 15V. I was following testflite video and that's what they did, but I guess they mislead me. ;( I bought a new RX and FC just now.
From now on do I even need to connect FC to the PDB or can I just use one of the ESC's red wire to provide 5V to FC? I just want it to get flying for once.
I'm pretty sure FliteTest build videos are quite correct or else the user community would have pointed out problems long ago. I've not seen a FliteTest video where they incorrectly wire up power to the flight controller or RX.
Unfortunately, there are so many options for equipment out there, it would be hard to document all the variances with different combinations of PDB's, ESC's, flight controllers, etc.
There are basically two types of power distribution systems: regulated vs unregulated power distribution systems.
With the regulated version, you don't need to supply your own BEC (or use ESC's with BEC's) and you can directly solder your FC/RX directly to the regulated output on the power distribution board.
With the simpler unregulated version, you will need to supply your own power regulator to power up those devices that only work on a set voltage (generally, FC's, RX's, servos, some cameras, some LED's, etc). That regulated power can come from a BEC (or ESC with BEC).
If you're going to use the same equipment you have in that picture you posted, I would probably not bother connecting the regulated output from the PDB to your FC/RX. Just use one of the ESC's BEC output to power your FC/RX. That'll keep it somewhat simple while allowing you to use your existing equipment.
