The article talks about "Deflation in the unit of account". The assumption is for a future world where bitcoin with a fixed and decreasing supply has replaced fiat and it, supposedly, results in lesser and lesser amount of currency being available to cater to wage requirements.
This also assumes that wages cannot be lowered as they are "sticky". That is, workers/ people want wages to increase, not decrease. (in absolute terms)

The way i am understanding this in very layman terms is that "There won't be enough BTC to distribute for everybody because it's supply is decreasing with time".
This looks like a compulsive argument. What if the majority holders just decide to HODL all of the BTC and never spend it?? What if they just decide to die fiat-less and leave their bitcoin stored on the blockchain with the private key destroyed.. Is it that kind of a scenario..??

What if BTC is the verifiable standard against which other currencies are pegged like they have always been against USD? It would be so much better if these economists were a little more open-minded and focused on informing public about how a publicly audit-able reserve currency would benefit the banking system. This would be a much better use of their time than trying to find such silly excuses against BTC.