Sometimes horses do this when they freeze and then remember to breath (sometimes accompanied by a startled reflex like they are mentally somewhere else

in our family Geronimo is the most manipulative (in a good way) in the ways he trained me for a recall
when i am in the house and he cannot see me he will call (whinny as this is not a Höhöhöhö but a Hiiiiiihiiihiihii)
if i am already out and about but not in the paddock or when all the horses come to greet me he will deliberately walk to the closest pedestal / seesaw / stone that he can station on and will wait - and i am super obedient and will come in and give him a treat / scratch.

over here Pipo learned too that if he will whinny at the gate there is a good chance i'll come out of the house with a treat for him.
this is rather new and still not constant (maybe happened 3 or 4 times only in the last 2 weeks) a funny thing about it that his whinny is so weird (the first time i herd it i wasnt sure it is a whinny at all - as if he still need to work on that and perfect it.

Tequila, Hercules and Boten are more of a Höhöhöhö people
Tequila will actually use it (like you described - as a tool) to call me out of the house - mostly when she thinks i took my time between hay meals
Hercule and Boten will mostly use it to show they approve when i am already coming
Hercules once used his whinny to call me out - which was very unusual - when Pipo's leg got caught in the hay net and he needed saving and Hercules was next to him calling me out. so i think he understand the concept too, just find it less useful to have me out.