Amplitech Group Inc (AMPG)

[JMD NY]

If you read their data sheet more carefully.
They say, “Noise figures as low as 2K are possible”
Which implies they have no test data at 4 Kelvin temperatures.

Then they say they are using PHEMT Technology. PHEMT Devices cannot achieve a Noise Temperature value of 2K at a 4 Kelvin base temperature.