A very false notion it is. It has been written nowhere and said nowhere that it is only priests and religious that can teach about the Scriptures and take Scripture classes.
As Christians, the Great Commission is the instruction of Jesus Christ to His disciples to preach and spread the Gospel to all the nations of the world (Matthew 28:19-20 and also cf. Luke 9:1-27). We are the disciples of Christ Jesus hence we are all mandated to live His Gospel and to preach it.
Often times, I have wondered why whenever we see a devout Christian who always preaches and teaches about the Scriptures, we are quick to assume that the person is either a priest or a nun or is aspiring to be one. Christians who realise that we are all called to preach the Gospel would go out of their way to carry out this obligation (religious or not).
There are even times when we see a lay faithful teaching the Scriptures so well, even far better than priests. So, this tells us that there are a number of lay faithful who are well-grounded in the Scriptures. There are many opportunities for lay faithful to teach the Scriptures such as teaching them in societies, during programs, Sunday schools, seminars and so on.
So, we are all called to be true heralds of the Gospel without exception.