Peopling of Eurasia and origins of haplogroup K and P.
If You follow genetic forums You probably had noticed unusual theories placing the homeland of haplogroup K or K2 in South East Asia and by consequence the haplogroup P would have moved to Siberia via the China. While later P supposedly moved to west in the form of R and Q. There is no much evidence for this theory but it is still there. So let's see what aDNA tells us.
We have quite old cases of haplogroup P from NE Russia (site Yana). And we have the occasion to check their autosomes and possible route of migration. Those samples are dated to 33.000 years ago so for modeling them we would need more older sources to avoid the effect of shared ancestry. I chose the available Upper Paleolithic samples from Eurasia. Unfortunately no such a sample is available from West Asia.
As You can see the fit is decent for Upper Paleolithic samples. It's clear from the model that Yana people had predominantly Western Eurasian Upper Paleolithic ancestry. They almost certainly migrated to North East Russia from/via the Central Asia.
They have also some China Tianyuan ancestry. Tianyuan is a 40.000 year old sample from North China. So it's quite possible that the first settlers of Siberia had some contacts with Paleolithic North Chinese populations, but this do not mean that they came from China.
It's remarkable that the paper discussing those samples says the same thing. G25 gives the same result as academic tools. So it should not be surprising that the paper says nothing about a migration via SE Asia.
Even more interesting is that the most important source of ancestry is the Vestonice16 which is associated to Gravettian culture and not more older BachoKiro and more proximate Ust-Ishim from Russia.
In the distance charts You can see that Yana and Tianyuan are from different worlds. It seems Tianyuan moved there from South ( although it's possible that it has a different route ) while Yana moved to Siberia from Western Eurasia.
As for the presence of minor branches of P in South East Asia they are simply a result of minor migrations from Western Eurasia to Indochina via the India. See the Yfull https://www.yfull.com/tree/K/