Sometimes it's best to learn the hard way because that makes sure the lesson sinks in. Had you just gone with the directions for that concentrate you'd probably be showing off some nice healthy plants instead of going "Oh crap".
Using too much is extremely common but the real problem is when one has overfed and the plants show signs of deficiencies. Then people have a tendency to add more stuff which makes things worse.
That guy is one of the biggest hacks on youtube. Why do you want to grow like him? This is a screenshot from one of his videos. I don't understand how anyone could listen to that clown when all his plants are nasty burned up plants. They're crispier than KFC extra crispy.