If you watch closer you’ll see someone attempt to climb up but is pulled back
I can’t see that in the RSBN video, at 1:45:45 he turns abruptly to the right as he senses a threat toward the right rear of the stage and 1 second later the SS man comes up and gets between Trump and that area. But I think you’re right as he clearly reacted to something he felt and maybe heard. The SS men responded extremely quickly, true pros.