Heather Net should better go back to her networking course.

Well that’s how floating point units work.

The following is more a explanation about the principle than a precise description of float values in programming, since working with binary values has its own quirks, especially with values lower than one, but anyways:

Think about a number noted by a base and an exponent, like
1.000.000
can be represented as 1*10^6.

1.000.001 now becomes 1,000001*10^6.

If you want more precision or bigger numbers maintaining the same precision, you will have to add further and further decimal places and that hits a limit at a certain amount.

So basically you can either get really high numbers in a floating point unit or you can store really precise small numbers. But you cannot achieve both at the same time.

I share that concern and would not rely on my messaging being secure. Anyways as far as they state it themself, your private key for decrypting should stay on your device (in fact it uses the signal protocol and does a few more steps, e.g. to implement shared sessions over multiple devices. You can have a look at their FAQ, they’ve linked a white paper within it describing the technical details). But the main question is in my opinion: do you trust the guarantees they give you? It’s the same struggle as with any proprietary software. You can trust them or you don’t, but you will never know without access to the source code.