It’s not said to be Priori Incantatem.
In the official screenplay, when Tina duels Graves, it’s never described as causing an instance of Priori Incantatem.
EXT. TIMES SQUARE—NIGHT
Graves is moving nearer and nearer to the Obscurus, which continues to scream and wail at his presence. He takes out his wand, poised . . .
Tina runs into view behind Graves. She fires at him, but he turns just in time, his reactions marvelous, astounding.
The Obscurus now vanishes. Graves, thoroughly irritated, advances on Tina, deflecting her spells with perfect ease.
Tina. You’re always turning up where you are least wanted.
Graves summons an abandoned car, which whooshes through the air, forcing Tina to dive out of the way, just in time.
By the time Tina has gathered herself up from the ground, Graves has Disapparated.”
- Fantastic Beasts and Where to Find Them (The Original Screenplay)
This likely means it’s not intended to be Priori Incantatem, since if it was, that’d likely be mentioned specifically in the official screenplay.
It’s likely their spells colliding.
It seems the filmmakers are using that particular effect to indicate spells colliding against each other in a duel, not wands locking together.
“More Killing Curses flew past Harry’s head from the two remaining Death Eaters’ wands; they were aiming for Hagrid. Harry responded with further Stunning Spells: red and green collided in mid-air in a shower of multi-coloured sparks and Harry thought wildly of fireworks, and the Muggles below who would have no idea what was happening –”
- Harry Potter and the Deathly Hallows, Chapter 4 (The Seven Potters)
A similar effect to what’s seen when Tina and Graves duel is used when Dumbledore and the Dark Lord duel, and Dumbledore has the Elder Wand, so his wand can’t possibly be the twin of the Dark Lord’s wand.
This is different than the effect used to show Priori Incantatem, which has a shimmery webbing surrounding the wizards whose wands’ twin cores are causing it to occur as well as their spells colliding, making it a distinctly different effect.
It’s likely that when Tina and Graves duel, it’s just their spells colliding, not their wands connecting in Priori Incantatem.