I think a bit of overreaching (which is what you did) is a good thing, that's how you introduce training stress that causes the body to adapt and become fitter. Just make sure the blocks of training that result in over-reach are balanced with some recovery (which doesn't have to mean complete inactivity, just backing off the intensity/volume a bit for a day or two can be sufficient).
I think "overtraining" has become a bit of a bogeyman that people worry too much about, and even use as an excuse to not push themselves to train harder. Full-blown overtraining (the kind that trashes your endocrine and immune systems) is something that happens over a period of months, not a week or two.
I have wondered about what you would call multi-day overreaching. If I ride very hard on Saturday, I should go for a recovery ride on Sunday, but if the weather is good and there's an interesting group ride on offer, I might do something demanding instead. I'll have tired legs and not ride with quite the intensity (or freshness) of Saturday, but still spend considerable time in Zone 4 or even Zone 5. This is a form of training stress, too, I suppose, and perhaps a net positive, but I some times wonder if I would build strength faster if I kept high intensity rides to isolated days (e.g., not the day before or after another high intensity ride). Of course, the professionals string together high intensity rides day after day, and though they are working from a level of fitness and stamina that I can only dream about, this does suggest that it isn't too harmful to go more deeply in to the red for a few days, and then rest/recover.