It's possible but fairly rare, given how most CUs set up their statement criteria.  The two statement types are independent as far as the criteria that determine whether a member gets a statement or not.  Typically a CU sets up their regular account statement to look at OC (open credit) accounts, which includes online credit cards, and produce a regular statement if there is any activity.  Likewise, a credit card statement is generally set up to produce a CC statement only if there is activity on the account that month. 

If your credit union set up your regular statement without specifying OC account activity as a condition of producing a statement, then assuming nothing else the member did that month made them eligible for a regular statement, they could get a credit card statement all by itself that month.