Use a multimeter and attach it to both pins. BEFORE you do that set it to DC test, start with a high voltage and then go down step by step. If you cannot measure any voltage it is at least unlikely that it is a capacitor.
Be careful with large capacitors btw. they can be deadly if charged and both poles are touched. they can charge themselves through the air over time.
I don't think it is a capacitor, but there is nothing that is impossible in electronics. (Apart from circuits never working on first test run ;-) )
OK, you could also test if that is a crystal by adding some external components and power and checking the signal or you can use a special crystal testing tool.
Then again you could simply open the device and see what is inside. Just consider that there could be some nasty stuff like acid or else inside. So if you really have no clue, in general, you should not open unknown components. They can contain almost anything from toxic metals, acids gas, radioactive material or precious metals
)).
Pandora's box.
Btw. Looks like a crystal to me.