This is absolute bunk - to put it politely. I did an article going over the types of carnivorous plants which could survive in vivaria (note: survive, not thrive) and which ones pose and do not pose significant dangers. I have raised carnivorous plants extensively. You can find the article here:
Carnivorous Plants in Terraria and Vivaria.
Even fully grown, large-cultivar (such as "Big Mouth") VFTs will not consume ("eat") an adult frog over 1/2". They may "grab" it, but not only is the frog strong enough to overpower the trap, the frog is "verifiably too large" to the plant, and it will re-open to avoid damage. Traps will not "seal" on most large, or "struggling" prey items. They aren't worth the effort or damage they will cause to the plant. Only a "newly morphed toadlet" sized froglet, frog or toadlet would be in danger. Beyond that, not all cultivars of VFT attain the sizes quoted - some cultivars are exceptionally small, and would have trouble closing on a wingless fruitfly. Of course, there are also cultivars that no longer "trap", so... it becomes a moot point of the hobbyist does their research.
The pitfall traps of plants like Darlingtonia, Heliamphora, Nepenthes and Sarracenia could pose a drowning risk to the frogs, but here's the kicker - numerous DF owners have reported their frogs BREEDING in the traps of pitcher plants, so I'm afraid the logic strikes out there as well. Large Sundews and Butterworts could pose a risk to a small DF, and juveniles due to their "flypaper" nature. Again, though - being flypaper they are poor choices for vivaria to begin with.