Maybe PLA uses 5 to refer to carrier based fighter aircrafts (e.g., J15). Perhaps PLA sees J35 to be one “generation” ahead of J20 in manufacturing techniques or strategic significance (that it deserves to be in the 30 category instead of 20) or it represents the next evolution of PLA Air Force planning so it is J35 instead of J25.
The 20 series like Z20, Y20, J20 (except for H20) call came out during 2010-2020, J35 will enter service between 2020-2030, it is one decade later, so being in the 30 category probably makes sense instead of being in the 20 category.
Finally who cares if its name is similar to F35, even if all Chinese war machines are directly copied from the US, as long as they can defeat Americans in wars that’s all that matters. These things are not made to score internet points, they’re used to kill. For example, you can laugh at PVA’s military equipment all you want but they killed a lot of Americans in the Korean War and that’s all that matters.
People need to do a bit of introspection and decolonize a their worldviews, what white people or Americans think and feel is meaningless. I wouldn’t care if my dog thinks J35 and F35 looks alike, unless I want to obtain approval and validation from my dog, but that would be stupid.