Thats a valid point - but these are all semantics. Theres no reason why it couldnt be that you cant get through security etc. without confirmation that you are clear of the virus dated within the previous couple of days. That has the disbenefit of meaning that people may still travel to the airport with the virus, though they wont be able to get on a plane.
The point, more specifically, is that leaving the middle seat free is purely a psychological gimmick, with no real benefit to passengers and significant costs to all parties.
If aviation is to get going again, it either needs a full release of restrictions (as in back to pre-virus days) or some form of control of passenger flows to avoid the virus getting on a plane in the first place (hence the idea above, and thousands of alternative methodologies along similar lines). A full release of restrictions is probably only likely once the virus has been all but eliminated (i.e. not soon). Some form of control could instead be implemented in short order, and get the economy moving again. But it needs to be robust.