While this could be what happened, I suspect otherwise.
For many years, those of us in the cryptocurrency fields have said never enter your keys on a computer. Generate them offline on a hardware device and let that be it. The person making this claim clearly had to enter unencrypted keys into a computer to put them into his laspass vault. There are a number of malware variants that specifically target keys and search things like input fields in web forms and clipboards for those keys.
For many years, those of us in the cryptocurrency fields have said never enter your keys on a computer. Generate them offline on a hardware device and let that be it. The person making this claim clearly had to enter unencrypted keys into a computer to put them into his laspass vault. There are a number of malware variants that specifically target keys and search things like input fields in web forms and clipboards for those keys.