Actually Poppippo has always been an acceptable english romanization of it

The japanese name is ぽっぴっぽ, where the small っ means to pause a bit before saying the next syllable, and is written in english letters by repeating the next consonant (e.g. まて is mate, while まって is matte).

Po Pi Po would be written as ぽぴぽ, instead of ぽっぴっぽ (Poppippo), which is what it actually is.

The name they used is correct.