Can the word “deceiving” stand for “positive”?

I was puzzled with the line “(President Lyndon Johnson’s) appearances can be deceiving,” in the Washington Post’s (April 2) article titled “President Lyndon Johnson did indeed attend an Easter Egg Roll” with a photograph showing President Johnson at an Easter event at the White House on May 7, 1964.

My confusion arose from the contradiction of the phrase, “Appearances (which can be taken as 'attendance') can be deceiving” and the picture evidencing the obvious appearance of President at the site.

“A March 29 Loop post said it appeared that President Lyndon B. Johnson had not attended any of the White House Easter Egg Roll gatherings. But appearances can be deceiving. Marilynn Eaton, whose husband William Eaton covered the White House during the Johnson years for UPI, sent us a signed March 30, 1964 photo of Johnson and some kids, including her daughters Susan and Sally — seen sitting at the far right of the stage.”

Why is it “deceiving,” not “positive” or “obvious” when appearnce / presence / attendance of Jonson were evidenced by a photograph?

OP correctly gets the appearance = attendance allusion, but that's just a lead-in to the writer's main purpose - "wordplay" based on the (surprisingly recent, but now commonplace) saying...

(That's the American corpus in Google Books. The British preference is the other way around)...

It's important to note that the writer only uses appearances for the sake of the wordplay. The saying should be understood here as meaning the March 29 Loop post gave misleading information (what it said appeared to be true was manifestly contradicted by a photographic record). In this highly contrived context, the word appearances simultaneously refers to LBJ's attendance and superficial/misleading presentation in press releases concerning his activities.

I find it interesting to note that appearances are deceiving/deceptive has been around a lot longer, as has may be. But in recent decades, can be has become the standard version.

The phrase “appearances can be deceiving” is idiomatic. It is a proverb meaning “things can look different from the way they really are”.¹

The word appearances there relates to the earlier instance of appeared. The deceptive bit is casting doubt on the veracity or accuracy of the “apparent” claim.

Your text is saying that the supposition or assumption that LBJ had not attended was a deceptive one, in that he in fact did so based on the photo evidence presented.