@Garrett **********
blood tests are usually antibody tests, they less accurate and are used to establish prior infection in a population. There is a substantial window period with them and they won't show positive until many days after a swab will.
The airport isn't using blood tests, it's using PCR swab tests. These are more accurate and return a positive sooner but they are not a new test, they are what Thailand has been using since the start. They may just have sped it up a bit. I don't think it ever took "weeks" here though, maybe in the US in some places early on but it's a lot faster three now too.
"The lab is equipped to conduct polymerase chain reaction [PCR] tests, which provides up to 95 per cent accurate result within 90 minutes"
There is no indication that this will be a mechanism to skip quarantine, for the groups that require it. Maybe this is for the few day businessmen/government invitations who do get to skip it.