in response to the original post -
_luckily_ i get that kind of stuff all the time. at least twice a month maybe? sometimes more often than that. (unfortunately i've never had the specific experience that you had). and most usually when practicing directly with sensei. the dojo i practice in is a USAF dojo.
maybe im just a weirdo, hmmm
occasionally it's a kind of thing that i dont even realize happened until later on in the day. sometimes there are big things that i notice right away. and yeah, sometimes a senior person will say they are going to do something specific and then would feel it right there, i guess in a way similar to what you felt. Jim Baker Sensei comes to mind...
i have found that people are already able to do these things. i mean beginning students. even though they may not know it yet, they move with ki during their techniques every now and then. when i try and stay sensitive to it sometimes i can pick out something that they're doing that feels funky but in a good way.
like you said, being open to it helps.
p.s. something makes me feel hesitant about sharing specific stories here. if you're interested in specifics, feel free to email me, firstname.lastname@example.org