Releasing the putter - what does that mean?

If you want a putter to hang from the hands, as he suggests, shouldn't it be shorter and with a more upright lie angle, because you don't want it to hang toe down at address?

Is it on when you let the natural arc of your stroke dictate the way you strike the ball. Not releasing putter is going straight back straight through when you have an arced stroke for example.

the video is speaking to what a 'release' is in a putting stroke as many folks get somewhat confused and assume it's something akin to a release with the hands that occurs in a golf swing - in putting terms the 'release' refers to the natural motion of the putterhead travel within the arc of the stroke

release really describes what happens to the putterheads motion, within the complete arc of the stroke as the face travels away from the ball then returns to and through impact into the follow through

folks who control and manipulate a straight back - straight through stroke do not 'release' the putterhead/face within a stroke they are using some kinda force to control the putters movement in a straight line - something that becomes more difficult to achieve the longer the putt's distance and the longer that stroke is - to keep it 'straight' to the line the putterheads arc has to be upwards and downwards arc

so in a natural putting arc (back and in to square to in and forwards) which occurs through the nature of human anatomy and the ball position being on the ground in front of the body - the putterhead will 'appear' to open as it goes back return to 'square' at impact and 'appear' to close in the follow through - but the face is always 'square' to the arc of the path

Stricker's putting posture with heel up, toe down putterhead mentioned to highlight the more extreme end of the wrist angle scale to help illustrate the point, as opposed to the normal wrist positions with the irons for full swings that are needed to encourage wrist action (set, lag and release)
Stricker also prefers to have the heel up than change the specs on his favorite putter

but the video is not putting this more extreme arched 'heel up' version forwards for all - if folks take in the whole vid you can see how the particular posture and wrist angles (arched with the head weight) has the putter at the lie angle to still be able to have the sole parallel to the ground, as in the putt at the end of the vid

a putting posture taken at set-up, along with distance from the ball can have forearms more akin to the plane of the putters shaft with the wrists 'arching' (ulnar deviation) without the heel being held off the ground
always advisable that the putters length & lie fits folks physicality allowing them to take good posture at set-up

Stricker though as an example shows folks still can, if they have a favorite stick they don't wish to alter specs on, find there are ways still to achieve more wrist arch to help stop involuntary wrist motion through the posture taken at set-up and distance to the ball - and folks also can choke down on the handle little ways