If we're being technical with the tag, it's not "love" triangle because the only love portrayed in this one-shot is that of Mao towards Yuki. But it's hinting at a possible true love triangle.
Those panels where Arashi is seen looking at Mao's face twice separately are deliberately placed there to hint of a romantic interest towards Mao regardless if she's yet to realize. It's the same as the last few panels where Yuki is zoomed in and her expression while seeing Arashi laughing with Mao could either be that she's had a realization about Arashi, or she's conflicted or jealous although it's quite established that she only sees Mao as a friend, successfully so.
Those panels aren't placed there randomly and this is the case with romance manga one-shots where exploration of feelings is limited. Try putting yourself to an author or filmmaker where you have to let a reader or viewer know of something relevant but you can't explore it further because of panel or time constraints--every panel/scene is important, others discarded.
If it wasn't hinted as a true triangle, those relevant panels wouldn't exist or at least their expressions wouldn't be the way they were, e.g. Yuki could've had a happy expression since two of her friends are finally getting along.