Thank you so much for your post and for sharing your other experiences! We Southern Baptists have a reputation for being quick to share our testimony and I cant help but wonder if it was one of us interrupting your class.
Personally, I've follow the "rule of thumb" to wait for the witness opportunity door to open, and then walk through:
But sanctify the Lord God in your hearts: and [be] ready always to [give] an answer to every man that asketh you a reason of the hope that is in you with meekness and fear: - I Peter 3:15
But, having said that, I do not wish to interfere with another Christians mission. I cannot know everything that God is doing in this world and thus, even with the best intentions, I could inadvertently work against His will by standing in the way:
Then Peter took him, and began to rebuke him, saying, Be it far from thee, Lord: this shall not be unto thee. But he turned, and said unto Peter, Get thee behind me, Satan: thou art an offence unto me: for thou savourest not the things that be of God, but those that be of men. Matthew 16:22-23
The Bible is so rich and deep! I am continually schooled by passages like those. Thanks.