Note that the 1.5% number above grossly overstates the percentage of migrants that are Chinese as it is computed based on the migrants encountered by the CBP.
Virtually all Chinese migrants coming through Mexico intend to seek asylum and so they actually look for the CBP to report in. On the other hand, migrants from most other countries have little chance of getting asylum and try very hard to avoid the CBP.
I want to add that the refusal rate of US B-visas (Non-immigrant) for Chinese nationals have also been steadily increasing over time,
This is corroborated , which is from the official State Department website. The total number of temporary visa issuances in general has also decreased from. I'm assuming 2023's numbers haven't recovered, especially with the B-visa refusal rate still being high.
My theory is that older, easier way for these people to migrate to the US would be to apply for one of the non-immigrant visas (which I'm assuming has a lower refusal rate than immigration visas) and then just overstay their visa. That's safer and not as expensive (you just need the money to apply for a visa and an airplane ticket). That's less of an option now because of the higher refusal rate, and it's easier to obtain political asylum (with a ).
So I don't believe the net number of yearly Chinese nationals migrating to the US has increased (more likely the opposite), it's just harder to go the easier route of overstaying a temporary visa, so they need to 走线 instead.