Dear Isaias,
for the first view the difference is in the dark colour flower.
The plant is more compact then the typical caudatum, has normally only 2, very seldom 3 flowers and a trapezoid staminode very differen to caudatum.
The last difference is the region where this species comes from, Middle-America, Guatemala.
It was in trade and culture many years as Phrag. warscewiczianum or caudatum var. warscewiczianum, then again described as Phrag. popowii.
Best greetings
Olaf