You are correct as there is a minor bending of the elbow. But, wait for the punchline. It is within the rules, the same rule that permitted Murali to bowl in Test cricket. Bowl, more like flick, similar to a sling shot. He took the most ever wickets by default. Warne was the best ever as he had a pure action.
Tbf I’m more inclined to call Bumrah out than Murali. Muralis elbow was bent the whole way through his action rather than extending (which is what the rules specify).
Bumrahs is hyperextension, and even though you can’t control that, I am sceptical that it’s under the allowed degrees of flexion.
Either way idc and they’re still both excellent bowlers.