Why is my boneless beef tough and unedible?
Without knowing the cut of meat, thickness, etc. it is very difficult to fully answer, but take a look at this chart for steaks:  http://chicolockersausage.files.wordpress.com/2012/01/cook-a-steak-blue-rare-medium-welldone.jpg (Putting link, not pic in case of copyright issues.)  To summarize though, a medium steak is about 135F and still has about 25% pink in it.  Med-well is about 150F and still has a hint of pink.  That is the highest you should be able to reach in a 150F oven and for many cuts would definitely be too tough for many people's tastes.  No pink at all is 160F plus, is not reachable in a 150F oven, and is almost always going to be dry and tough for most cuts.  Lamb chops number will be roughly the same.

Their comment on well done as being a waste of a quality steak is their statement, but one I and many others would share, and definitely towards a lamb chop.  I would never, ever intentionally cook one to no pink through, and certainly not without expecting it to come out dry, tough, and chewy.  I would also almost always sear before putting in the oven if at all possible to form a nice crust and help hold in some juices.

Now, as to your temp stated, a well done cut of meat, one with no pink through, is one that is 160F or more.  If you are really cooking at 150, this should not be possible.  The only way at that low of temp to get all pink out would be to cook so long that all liquids drain except possibly rendered fat.  If cooked for hours that way, something like a pulled pork or a pot roast might be tender, but only because most connective tissue has broken down.  A far more typical practice would be to sear-seal the meat first and the finish in a heated, higher temp oven to allow the meat to get to your desired temperature/doneness without cooking away all the precious fluids that allow it to stay tender.  You normally are cooking working muscle groups and they will very much have a tendency to become tougher the more you cook them unless using a method like braising that will start to break down the connective tissue with time.