Yes, you could call the present participle "been" a linking verb in that it has the noun phrase "a coincidence" as subjective predicative complement; compare "That was not a coincidence" where "that" = "a coincidence". And I assume by "helping verb", you mean "have". We usually call this "have" the 'perfect auxiliary', but you can call it a helping verb if you like.
Some other so-called linking verbs like "seem", "feel" and "keep" also occur in the perfect construction:
"He has seemed a little tense lately". (cf. "He is tense")
"Kim had felt lonely/like an intruder". (cf. "Kim was lonely/like an intruder")
"I have kept warm lately by wearing extra clothes". (cf. "I am warm")