As per Google:
MBAFF stands for Macroblock Adaptive Field/Frame encoding and is a feature in the H.264/AVC video standard that improves compression efficiency for interlaced video. It allows each pair of macroblocks to be encoded as either a single frame or two separate fields, which helps in preserving picture quality while reducing bit rate by intelligently adapting to static or moving content within the macroblocks. This is often found in modern interlaced content like Blu-rays and broadcasts, as it provides better quality than older field-only encoding methods.
Short version: even though its encoded/broadcast at 25fps, there is actually 50fps inside it.