[white2015]

?
Looks like a plug to me.
Strange

 

[white2015]

After zooming in
It does not look like a plug.
Maybe a gasket that is inside your spark plug socket.
To hold the plug when it is out of its threads.

 

[white2015]

Well then, how did they do a compression test? Can they use an adapter that doesn't screw into the spark plug hole threads?
After the compression test the OP tried to install the spark plugs and found the hole plugged up.
Unless he put his spark plug wrench into that hole BEFORE he put a spark plug in his wrench, I don't understand how that obstruction happened. Still, the helpful suggestions on how to remove, whatever it is, are good.
it will be interesting to see what it is and 'how' and 'when' it happened.
Some info definitely seems to be missing.
Buffalo4
PS: I guess that while he was installing sparkplugs in the adjacent cyls the rubber plug may have dropped out of the socket and into the hole. I would think he would have realized that when he put the spark plug in the socket to do that cyl, as it wouldn't stay in the socket without that rubber plug. 🤯

Maybe they did not really do the test.
Was the OP actually there?

 

[white2015]

Has anyone considered we may have a troll.

You all are eating this up, trying to figure it out.

The whole premise is impossible.
And everyone knows it.

JMTs

I may try this too now in the future.

Maybe I'm too old but I just can't fathom why anyone would take the time to post this as a troll reaction.
It's not like you are starting a honda vs toyota war and get to watch other posters be nasty to each other.
Why?