Namely, the Pig spawns the Temperate variant while the Frog spawns the Warm variant in the Mangrove Swamp, Desert, and Warm Ocean biomes, as well as all Nether biomes.

The Pig also spawns the Temperate variant in the Deep Frozen Ocean, Frozen Ocean, Frozen Peaks, Frozen River, Grove, Ice Spikes, Jagged Peaks, Snowy Beach, Snowy Plains, Snowy Slopes, and Deep Dark biomes, as well as all End biomes, while the Frog spawns the Cold variant.

While Pigs cannot spawn naturally in most of these biomes, they can spawn in some of them, and it can be useful for creators for the variants to line up.

This can be reproduced by going to any of the biomes mentioned and spawning a Frog and a Pig, spawn eggs and /summon yield the same results.