This definition is in error. "Weird" is an adjective, modifying a noun, or an adverb modifying an adjective modifying a noun. (E.g., "She appeared wearing a weird little hat.")
Adjectives and adverbs do not have participles, only verbs do. There is no verb "to weird," hence there is no participle.
In 2010 "weirding" is coming into use as a way to describe what seems to be happening to Earth's climate, as in "global weirding," as opposed to "global warming," which is in itself a misnomer. The term appears to have been introduced in a Nov. 7, 2002, New York Times article, "Bananas in the Back Yard." <http://www.doubletongued.org/index.php/dictionary/global_weirding/>
I'm sure of my facts here, but not sure enough of my right to edit someone else's entry. Therefore, I earnestly suggest that the definition might well be changed to "being or becoming weird."