Back in the days of netnews, store-and-forward email, private dialup BBSes, and a far lower proportion of script kiddies in cracker circles, there was concern that the government would be able to monitor (or already was monitoring) a larightrge amount of the Internet - netnews, mail, BBSes, etc., - and handle the volume by using keyword-searching software. (Snowden's recent revelations show their concerns were correct - through PERHAPS a bit early.) So some among the computer underground began obfuscating their text communications to try to stymie that approach to surveillance.
In addition to using slang (which, of course, would quickly be figured out), the approach was to distort the spelling of words in ways that (with a little effort) would be recognizable by a human eye but not by a straightforward word matcher. Misspellings (common, adjacent-key, adjacent-character substitution, etc.), homonyms, substitution of letters that looked similar, digits and punctuation for similar-looking letters (such as 3 for E, dyslexic style), building typewriter pictures of letters, etc. were typical. The idea was to pile distortion upon distortion until it was somewhat difficult to read, and constantly mutate the distortions, perhaps settling on a style but NOT on something that could be easily built into a pattern-matching.
Thus was born leet-speak (always, of course, spelled in its own form, such as "133t" or "I334".) Of course the constant-mutation was quickly lost in favor of more stable use of certain attractive forms, thus turning it into an ordinary slang and defeating the purpose.
At the time "owned" was already a slang term applied to systems which were cracked and controlled by a tacker, or the owner/operator of such systems. "pwned" falls right into the pattern on two rules: adjacent-key misspelling and "little p looks like little o" visual pattern matching. So I assumed, at the time, that it was just another instance of the form.
Now that does not say that it DIDN'T originate as an in-game typo that grew into an in-joke. But gaming and cracking circles have overlapped substantially since the breaking of early attempts at computer-game copy protection. So the two explanations are not in conflict:. A typo that fit right into the form would be immediately seized and used.