I assumed it to be a hardware wallet or a cold bitcoin storage
What you have described is neither a hardware wallet nor cold storage. It is a hot wallet which you turned off for a few months, and is only marginally more secure than a hot wallet which is always on.
In terms of the discussion about RDRAND and entropy sources, this is relevant:
Most good wallets will be based on entropy directly from the OS and the computer's hardware. Bitcoin Core, as an example, draws entropy from /dev/urandom (which is from the OS, or the equivalent on non-Linux systems), RDSEED/RDRAND (which is from the processor), and a whole host of data from the computer itself, such as current resource usage, timestamps, kernel parameters, network data, version data, etc. All of this is then combined through a variety of techniques such as XORs and hashes, so if one source of entropy is weak or compromised then your final result should still be secure.
You can read more in the code here:
https://github.com/bitcoin/bitcoin/blob/master/src/random.hhttps://github.com/bitcoin/bitcoin/blob/master/src/random.cppAnd of course, if you really don't trust any of this and still think your entropy might be compromised, then as BHC says, just flip a coin.