For the moment, I'm going to ignore the possibility that their patent actually covers something significantly different than your tracker, and just deal with the matter of dates.
They have 1 year following the invention within which to file the patent, so your invention would need to predate the patent by at least 1 year to qualify as statutory prior art.
As it stands right now, your invention might be prior art, but then again, it might not be. The question would come down to who actually invented it first. In most cases, that's translated as "who actually reduced it to practice first". For example if you had lab notes (or similar) showing when you'd first gotten your invention to work, that would be the crucial date. Obviously it must have worked for at least some short period of time before you demonstrated it. If you could show that it was more than 8 months before you demonstrated it (i.e., more than one year before they filed for their patent) then it would clearly invalidate their patent.
Just for the sake of argument, let's assume you had your device working 2 months before you showed it, so it predated their filing by six months. To show their patent was valid, they'd have to show that they invented it during the (approximately) six month period starting from a year before they filed, and ending the day you invented your tracker. Their patent could/would be valid if and only if they could show it was invented during that window.
In other words, what you've shown isn't necessarily enough to prove their patent is invalid. Without knowing the exact history of their claimed invention, and how long before filing they invented it, it's impossible to say whether the patent is valid or not.