*For Conductors*!!! Question about the Mendelssohn symphony No.5.?

In the last movement of the Mendelssohn 5th symphony, exactly 11 bars after K, that measure is written in 2, whereas the whole movement itself, is written in 4. Is there an official term from this type of writing??? Or would one consider this a sort of "cheat"? SERIOUS ANSWERS ONLY!!!!! Thank you:-)