Did the mechanic shoot in some oil in the cylinder that was "dead" to see if it built up pressure or not? Didn't happen to pull the CEL by chance did you?
Hard to say at this point, could be anything from a holed piston, to blown headgasket, to dropped valve, cracked piston ring, etc. Almost have to open it up to assess the situation, not sure if a borescope or fibrescope will tell you that much in the meantime.
Double check the oil and coolant levels, see if any one of them looks "off" in color or odor. Look for the telltale signs of coolant in oil (looks like mayonnaise) - for oil in coolant, usually that forms a "slick" on the surface of the coolant reservoir, but that may not have made it to the top yet.
Interestingly is the pattern. Are those numbers form cylinder #1 - #4 or the other way around? If they were taken in order, since they are decreasing from one piston to the next piston (assuming he did a "dry" and "wet" compression test) - looks like it it could have been a blown headgasket or more likely the fuel pump died and leaned out, burning one or more of the valves, holed the piston top.