First of all: Yes, it is possible that your device is not sending at 433MHz, since other frequencies are written on it. Different countries have different regulations on different frequencies, so there are devices which could send on different frequencies.
There are several possible problems here.
433MHz is not a single frequency, it is a frequency band with a (not so large) frequency range. Transmitters can send on one of the frequencies, like radio stations. Their transmitter listens on that frequency, just like a radio.
Then, there are many ways to transmit data.
The most simple one for 433MHz is to switch the sender on and off (ASK, Amplitude Shift Keying). Compare this to AM radio where the sender sends on a fixed frequency, and varies amplitude to transmit sound. The problem is: When the sender is far away, one hears lots of noise, especially when there is silence in the sound. However, this is how the majority of devices communicate.
A more advances transmitting technique is to keep the sender on, but change between two frequencies (FSK, Frequency Shift Keying). This is like FM radio. Think about: If there is no radio station on the selected frequency, you hear loud noise, but once you tune to a station, the sound is very clear, and even silence is real silence. The quality is much better here, even if the station is far away.
Now, back to your 433MHz receiver.
As a very cheap one, it can not tune to a specific frequency, but receives the entire band. It is possible that it doesn't receive a weak sender, like it's hard to understand a quietly speaking person in some distance on a party. Solution: Put the sender next to the receiver.
And since the receiver is of the ASK type, it can not receive a FSK sender. A FSK sender appears as "always on".
Next: If you don't hear anything on the radio, you increase volume until you hear noise. If then there is a transmission, it's very loud, and you decrease volume, until it's ok. If the transmission is over, well, YOU would keep the volume setting since you expect the next transmission at the same level. The receiver always increases volume slowly until it "hears" something, even if it's noise.
If you look at your GPIO with Piscope, you should see a stream of random ones and zeros. As soon as something is received, you should see some pattern. This is the prove if your receiver is properly working.
If it does, it's still possible that RFsniffer does not understand the pattern sent by your sender, like you don't understand every language. There are common standards out there, but some senders implement their own, and then, RFsniffer is lost.
