I think for that response the mechanic had blocked the passenger valve breather just to eliminate air leaks for the maf but its not a good practice even as a test.
passenger valve cover breather must always be open to air, or rerouted back to the turbo intake pipe. you can also use a catch can or just run a breather on the valve cover but depending on how much oil your motor spits out it may get the bay all dirty not using a can. every motor is different.. amount of boost you run, piston ring wear, turbo drain issues, oil pressure from using wrong oil pump (gte on GE) will all effect how much crank case pressure the motor builds and thus have to escape via the breather or blow out your front and rear main seals. the more pressure also the more oil its gonna take with it, which is why some have to use a can. a proper setup on a healthy motor will minimize this pressure and you can get away with just a breather on the valve cover.
normal practice is to leave PCV in place on drivers side, and put a filter on the passenger side.. or put a line to a catch can with a filter on it, or a line to a catch can and another line to turbo intake pipe, or a line just straight to the turbo intake pipe (might get most oil in your intercooler/piping this way also reduces octane more oil that goes through).
so there are lots of was to do it but the main idea is that the passenger side is always open to air wether its through a hose or a catch can or the turbo intake pipe. it should never see boost so it cannot go in intercooler piping.
IF you have a map sensor setup like JDM ecu, its simpler because you can just run a breather on it or a catch can with a breather. we do not have to worry about metered air.
IF you have a maf sensor setup (USDM or obd2), then its more complex because it needs to be metered and that means routing it to the turbo intake pipe after the maf but before the turbo. you can use a catch can inline but no air can be released to have the right amount of air measured.
this is what they were doing in the quote you quoted me on, and since it was a maf setup it does need to be recirculated, so the mechanic decided to just block it off temporarily and that is a major no no if you block the passenger side and have the pcv on the drivers side, you have completely blocked the motors ability to vent pressure and you will blow your seals likely the first time you build crank case pressure. It should never be blocked off even for a test in my opinion.
IF you need extra evacuation, you can remove the PCV from the drivers side and tap the valve cover for a fitting and run that side also to a can or use a breather on it. I have a thread showing how.
this is the crazy passenger side valve cover I may use someday with 2 breathers on it. remember the more pressure you can relieve at once the less oil that will come up with it.