From what you describe, I'd guess that something about that key is damaged...under the keys, there is a membrane and connections. If, for example, that membrane is compressed and the connection is very very close, then just touching the key could perhaps complete the connection and execute the key press. But, in any event, this sounds definitely like a hardware issue, which is pretty much impossible to truly diagnose at an internet distance, and really impossible to resolve at that distance.
If you remain in warranty, I recommend you seek formal support under those terms. If you are out of warranty, I recommend you find a local (to you) shop with a qualified BB hardware technician to give you a proper diagnosis and estimate.
Occam's Razor nearly always applies when troubleshooting technology issues!
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