Was the ski lift snowboarding event the first time?
Do you get any other symptoms on the outside of the lower leg or the foot such as pins and needles, shooting (like an electric shock) pains?
Whether you do or not what first came to mind was that you may have given yourself a compression injury of the Superficial Peroneal nerve. This could be so even if you don't get the above symptoms but any of the above symptoms would add weight to this conjecture. this particular nerve runs down the side of your lower leg and gives the "power supply" to the two muscles that turn your foot outwards (Peroneus longus and brevis). It also supplies sensation to the skin on the outside of the lower leg and over the back of the back of the foot. The business of positioning your foot on the motorbike peg may be stretching the nerve at the same time as the boot is pinching the nerve . We call this "adverse neural tension" and it is often a combination of pinching and stretching that really gets it going. Relieving the pain by resting the heel on the peg may change the position of the ankle joint and thereby relieve the amount of stretch on the nerve.
Nerves are extremely delicate tissue as well as being of immense value to the body. So nature provides a protection of making the outside of the nerve very sensitive to anything that may potentially injure the nerve. Sort of a warning signal - and the warning signal is marked pain - " OI! DON'T TOUCH! ME". Once irritated it can be very easily stirred up - out of all proportion to the force you apply to annoy it.
In contrast muscles and tendons are fairly robust tissues and are not likely to be bothered by the wearing of a boot unless there was some fairly major trauma to the area.
How sure am I? 70-80%. The nerve doesn't run exactly where you described it - tends to be on the outside but a bit more towards the front than the back - Still sounds like it could be close enough to be the problem. There is also a lot of normal variation of exactly where these nerves lie. It could be you are unlucky to have part of the nerve very close to the surface where it can be sandwiched by pressure between the boot and possibly the underlying bone (the fibular) and the covering around the muscles. Another touchy point is when the nerve is sandwiched between layers of muscles.
I suggest you get it checked out. If I am right treatment options may be:
* a careful and skillful mobilisation of the nerve - This is a gentle manipulative therapy procedure but this has to be within what the nerve can handle.
* Some minor alteration to the shape of the boot may relieve the pressure may prevent it happening. Your physical therapist could advise you.
You have to get the pressure off the nerve. Every time you irritate it you are just making matters worse.