The answer is big endian, the MSB is stored in the lowest address.

I can understand the confusion for Intel made quite a mess out of the 8051 in this respect.
- 16 bit operands use big endian.
- DPL and DPH are stored in little endian
- TL0, TL1, TH0 and TH1 are completely mixed

Why does Intel call it a "logical" circuit anyway?

The same mess is created with some control bits as well.
- Most multi bit settings are with MSB first
- Serial mode bits SM0 and SM1 are just the other way around!

Happy programming