Using Existing Circuit for LEDs

Hello all -

Electrical newb here, and new to the forum but long-time DIY'er, so full disclosure up front. I will note my local fire taxes are paid up!

That said, I installed a row of new LED in-ceiling lights meaning to use an existing in-ceiling circuit to power them. The previous usage had been a ceiling fan and was switch-controlled from one wall location. The ceiling fan had two romex 14/2 cables running to/from it. I wired them to the new LEDs (blacks to blacks/whites to whites/greens to greens) and turned on the breaker. The lights are on when the switch is in the off position, and if I flip the switch 'on' it trips the breaker.

I've done this kind of thing multiple times in the past with success but suspect I have run into a type of circuit that I haven't run into before.

With the cables disconnected and the breaker on, both sides of the circuit appear hot when tested.

Both cables are 2-wire 14/2 romex (black/white/green).

Thanks for any insights!

CTWE