Based on some reasonable evidence. Those "donuts on a rope" trails are consistent with pulse detonation engines.
We already know that this stuff is trying to be hypersonic, and that is within the capabilities of what is known about this technology. We also know about quantum radar, and various other exotic and advanced technologies.
Some of what they are doing can be extrapolated from what is known and what we currently understand about physics.
“some reasonable evidence” found where?
“can be extrapolated” or in other words, speculated about.
“We also know about quantum radar” - we still trying to figure out quantum computing, but already have a quantum radar?
There are pulse detonation rocket engines, but no proof that they are in any plane, just the assumption, as is the contrail pictured - rocket or plane?
Most of this is pure speculation couched in other terms.